diff --git a/src/app/shared/btn-disabled.directive.ts b/src/app/shared/btn-disabled.directive.ts
index 427d1654da0..bbc21fef7f8 100644
--- a/src/app/shared/btn-disabled.directive.ts
+++ b/src/app/shared/btn-disabled.directive.ts
@@ -59,5 +59,19 @@ export class BtnDisabledDirective {
         event.stopImmediatePropagation();
       }
     }
+
+    /**
+     * Prevents the default action and stops the event from propagating when the element is disabled.
+     * Some controls (e.g. dropdown options) commit on mousedown rather than click, so a disabled
+     * element must ignore mousedown as well to stay non-interactive.
+     * @param event The mousedown event.
+     */
+    @HostListener('mousedown', ['$event'])
+  handleMousedown(event: Event) {
+    if (this.isDisabled) {
+      event.preventDefault();
+      event.stopImmediatePropagation();
+    }
+  }
 }
 
diff --git a/src/app/shared/form/builder/ds-dynamic-form-ui/models/scrollable-dropdown/dynamic-scrollable-dropdown.component.html b/src/app/shared/form/builder/ds-dynamic-form-ui/models/scrollable-dropdown/dynamic-scrollable-dropdown.component.html
index be852fbcbcc..eb523d91c58 100644
--- a/src/app/shared/form/builder/ds-dynamic-form-ui/models/scrollable-dropdown/dynamic-scrollable-dropdown.component.html
+++ b/src/app/shared/form/builder/ds-dynamic-form-ui/models/scrollable-dropdown/dynamic-scrollable-dropdown.component.html
@@ -49,6 +49,7 @@
       </button>
       <button class="dropdown-item collection-item text-truncate" *ngFor="let listEntry of optionsList; let i = index"
               [class.active]="i === selectedIndex"
+              [attr.aria-selected]="inputFormatter(listEntry) === (currentValue | async)"
               [dsBtnDisabled]="isOptionDisabled(listEntry)"
               (keydown.enter)="selectEntry(listEntry, sdRef)" (mousedown)="selectEntry(listEntry, sdRef)"
               title="{{ inputFormatter(listEntry) }}" role="option" type="button"
diff --git a/src/app/shared/form/builder/ds-dynamic-form-ui/models/scrollable-dropdown/dynamic-scrollable-dropdown.component.ts b/src/app/shared/form/builder/ds-dynamic-form-ui/models/scrollable-dropdown/dynamic-scrollable-dropdown.component.ts
index bef1db4460a..d5ec8e44996 100644
--- a/src/app/shared/form/builder/ds-dynamic-form-ui/models/scrollable-dropdown/dynamic-scrollable-dropdown.component.ts
+++ b/src/app/shared/form/builder/ds-dynamic-form-ui/models/scrollable-dropdown/dynamic-scrollable-dropdown.component.ts
@@ -216,6 +216,10 @@ export class DsDynamicScrollableDropdownComponent extends DsDynamicVocabularyCom
     }
   }
 
+  /**
+   * Build the set of canonical identities already selected in the OTHER rows of
+   * the same repeatable field, so those options can be disabled/skipped.
+   */
   private getUsedSiblingValues(): Set<any> {
     const used = new Set<any>();
     const parent = this.model.parent;
@@ -226,8 +230,7 @@ export class DsDynamicScrollableDropdownComponent extends DsDynamicVocabularyCom
           rowGroup.group
             .filter((siblingModel) => siblingModel.name === this.model.name)
             .forEach((siblingModel) => {
-              const value = (siblingModel as any).value;
-              const canonical = typeof value === 'string' ? value : value?.value;
+              const canonical = this.canonicalKey((siblingModel as any).value);
               if (isNotEmpty(canonical)) {
                 used.add(canonical);
               }
@@ -237,11 +240,31 @@ export class DsDynamicScrollableDropdownComponent extends DsDynamicVocabularyCom
     return used;
   }
 
+  /**
+   * Canonical identity of a vocabulary value/entry used for duplicate detection.
+   * For authority-controlled vocabularies (e.g. Funder) the authority is the
+   * stable identity; otherwise the plain value is used. A bare string value is
+   * returned as-is.
+   */
+  private canonicalKey(entry: any): any {
+    if (isEmpty(entry)) {
+      return null;
+    }
+    if (typeof entry === 'string') {
+      return entry;
+    }
+    return isNotEmpty(entry.authority) ? entry.authority : entry.value;
+  }
+
   isOptionDisabled(entry: any): boolean {
-    return hasValue(entry) && this.usedSiblingValues.has(entry.value);
+    const canonical = this.canonicalKey(entry);
+    return isNotEmpty(canonical) && this.usedSiblingValues.has(canonical);
   }
 
   selectEntry(entry: any, sdRef: NgbDropdown) {
+    // Refresh against the live sibling values first, so a value that was chosen
+    // in another row after this dropdown was opened is still blocked at commit.
+    this.usedSiblingValues = this.getUsedSiblingValues();
     if (this.isOptionDisabled(entry)) {
       return;
     }
@@ -278,7 +301,12 @@ export class DsDynamicScrollableDropdownComponent extends DsDynamicVocabularyCom
       event.preventDefault();
       event.stopPropagation();
       if (sdRef.isOpen()) {
-        this.selectEntry(this.optionsList[this.selectedIndex], sdRef);
+        // Guard against selecting a stale/undefined entry while options are still
+        // (re)loading after a keyboard filter keystroke.
+        const candidate = this.optionsList?.[this.selectedIndex];
+        if (!this.loading && hasValue(candidate)) {
+          this.selectEntry(candidate, sdRef);
+        }
       } else {
         this.openDropdown(sdRef);
       }
diff --git a/src/app/shared/form/builder/ds-dynamic-form-ui/models/scrollable-dropdown/dynamic-scrollable-dropdown.repro.spec.ts b/src/app/shared/form/builder/ds-dynamic-form-ui/models/scrollable-dropdown/dynamic-scrollable-dropdown.repro.spec.ts
new file mode 100644
index 00000000000..1005a01df25
--- /dev/null
+++ b/src/app/shared/form/builder/ds-dynamic-form-ui/models/scrollable-dropdown/dynamic-scrollable-dropdown.repro.spec.ts
@@ -0,0 +1,262 @@
+// Reproduction spec for PR #26 reported issues:
+//  Issue 1: duplicate value can be added after deleting a row.
+//  Issue 2: opening the dropdown and clicking outside (blur) clears selected value(s).
+//
+// This spec uses the REAL @ng-dynamic-forms DynamicFormArrayModel semantics
+// (parent wiring, removeGroup/insertGroup reindex) that the production form builder uses.
+import {
+  ChangeDetectorRef,
+  CUSTOM_ELEMENTS_SCHEMA,
+  Injector,
+} from '@angular/core';
+import {
+  ComponentFixture,
+  fakeAsync,
+  TestBed,
+  tick,
+  waitForAsync,
+} from '@angular/core/testing';
+import {
+  FormsModule,
+  ReactiveFormsModule,
+  UntypedFormControl,
+  UntypedFormGroup,
+} from '@angular/forms';
+import { NgbModule } from '@ng-bootstrap/ng-bootstrap';
+import {
+  DynamicFormArrayModel,
+  DynamicFormLayoutService,
+  DynamicFormsCoreModule,
+  DynamicFormValidationService,
+} from '@ng-dynamic-forms/core';
+import { DynamicFormsNGBootstrapUIModule } from '@ng-dynamic-forms/ui-ng-bootstrap';
+import { TranslateModule } from '@ngx-translate/core';
+import { InfiniteScrollModule } from 'ngx-infinite-scroll';
+
+import { APP_DATA_SERVICES_MAP } from '../../../../../../../config/app-config.interface';
+import { VocabularyEntry } from '../../../../../../core/submission/vocabularies/models/vocabulary-entry.model';
+import { VocabularyOptions } from '../../../../../../core/submission/vocabularies/models/vocabulary-options.model';
+import { VocabularyService } from '../../../../../../core/submission/vocabularies/vocabulary.service';
+import { NotificationsService } from '../../../../../notifications/notifications.service';
+import {
+  mockDynamicFormLayoutService,
+  mockDynamicFormValidationService,
+} from '../../../../../testing/dynamic-form-mock-services';
+import { NotificationsServiceStub } from '../../../../../testing/notifications-service.stub';
+import { VocabularyServiceStub } from '../../../../../testing/vocabulary-service.stub';
+import { FormFieldMetadataValueObject } from '../../../models/form-field-metadata-value.model';
+import { DsDynamicScrollableDropdownComponent } from './dynamic-scrollable-dropdown.component';
+import { DynamicScrollableDropdownModel } from './dynamic-scrollable-dropdown.model';
+
+const SD_TEST_MODEL_CONFIG = {
+  vocabularyOptions: {
+    closed: false,
+    name: 'common_iso_languages',
+  } as VocabularyOptions,
+  disabled: false,
+  errorMessages: { required: 'Required field.' },
+  id: 'dropdown',
+  label: 'Language',
+  maxOptions: 10,
+  name: 'dropdown',
+  placeholder: 'Language',
+  readOnly: false,
+  required: false,
+  repeatable: true,
+  value: undefined,
+  metadataFields: [],
+  submissionId: '1234',
+  hasSelectableMetadata: false,
+};
+
+const entry = (v: any, display?: string) =>
+  Object.assign(new VocabularyEntry(), { authority: v, display: display ?? ('e' + v), value: v });
+
+/**
+ * Build a repeatable DynamicFormArrayModel and wire each child model's `parent`
+ * to its group, exactly like the library's createFormArray/createFormGroup does.
+ */
+function buildArray(count: number): DynamicFormArrayModel {
+  const arrayModel = new DynamicFormArrayModel({
+    id: 'dropdownArray',
+    groupFactory: () => [new DynamicScrollableDropdownModel(SD_TEST_MODEL_CONFIG)],
+    initialCount: count,
+  });
+  arrayModel.groups.forEach((g) => g.group.forEach((m) => ((m as any).parent = g)));
+  return arrayModel;
+}
+
+/** Faithful to DynamicFormService.insertFormArrayGroup: insertGroup + createFormGroup(parent). */
+function addRow(arrayModel: DynamicFormArrayModel, index: number) {
+  const g = arrayModel.insertGroup(index);
+  g.group.forEach((m) => ((m as any).parent = g));
+  return g;
+}
+
+/** Faithful to DynamicFormService.removeFormArrayGroup (model side): removeGroup(splice+reindex). */
+function removeRow(arrayModel: DynamicFormArrayModel, index: number) {
+  arrayModel.removeGroup(index);
+}
+
+describe('REPRO PR#26 – duplicate + clear-on-blur', () => {
+  let fixture: ComponentFixture<DsDynamicScrollableDropdownComponent>;
+  let comp: DsDynamicScrollableDropdownComponent;
+  const vocabularyServiceStub = new VocabularyServiceStub();
+
+  beforeEach(waitForAsync(() => {
+    // Options available: value 1 ('one') and value 2 ('two') from the stub.
+    vocabularyServiceStub.setNewPayload([
+      Object.assign(new VocabularyEntry(), { authority: 1, display: 'one', value: 1 }),
+      Object.assign(new VocabularyEntry(), { authority: 2, display: 'two', value: 2 }),
+      Object.assign(new VocabularyEntry(), { authority: 3, display: 'three', value: 3 }),
+    ]);
+    TestBed.configureTestingModule({
+      imports: [
+        DynamicFormsCoreModule,
+        DynamicFormsNGBootstrapUIModule,
+        FormsModule,
+        InfiniteScrollModule,
+        ReactiveFormsModule,
+        NgbModule,
+        TranslateModule.forRoot(),
+        DsDynamicScrollableDropdownComponent,
+      ],
+      providers: [
+        { provide: NotificationsService, useValue: new NotificationsServiceStub() },
+        Injector,
+        ChangeDetectorRef,
+        DsDynamicScrollableDropdownComponent,
+        { provide: VocabularyService, useValue: vocabularyServiceStub },
+        { provide: DynamicFormLayoutService, useValue: mockDynamicFormLayoutService },
+        { provide: DynamicFormValidationService, useValue: mockDynamicFormValidationService },
+        { provide: APP_DATA_SERVICES_MAP, useValue: {} },
+      ],
+      schemas: [CUSTOM_ELEMENTS_SCHEMA],
+    });
+  }));
+
+  /** Bind the component under test to a specific row model of the array. */
+  function bindComponentToRow(rowModel: DynamicScrollableDropdownModel) {
+    fixture = TestBed.createComponent(DsDynamicScrollableDropdownComponent);
+    comp = fixture.componentInstance;
+    comp.group = new UntypedFormGroup({ dropdown: new UntypedFormControl() });
+    comp.model = rowModel;
+    fixture.detectChanges();
+  }
+
+  const fakeRef: any = { open: () => undefined, close: () => undefined, isOpen: () => false };
+
+  it('SANITY: sibling value is disabled in a fresh 2-row array', fakeAsync(() => {
+    const arr = buildArray(2);
+    (arr.get(0).group[0] as any).value = entry(1);        // row0 -> value 1
+    bindComponentToRow(arr.get(1).group[0] as any);        // component = row1
+    comp.openDropdown(fakeRef);
+    tick();
+    expect(comp.usedSiblingValues.has(1)).withContext('value 1 used by row0').toBeTruthy();
+    expect(comp.isOptionDisabled({ value: 1 })).withContext('option 1 disabled').toBeTruthy();
+    expect(comp.isOptionDisabled({ value: 2 })).withContext('option 2 free').toBeFalsy();
+  }));
+
+  it('ISSUE 1a: after deleting the MIDDLE row and adding a new row, still-present values must stay disabled', fakeAsync(() => {
+    const arr = buildArray(3);
+    (arr.get(0).group[0] as any).value = entry(1); // A=1
+    (arr.get(1).group[0] as any).value = entry(2); // B=2
+    (arr.get(2).group[0] as any).value = entry(3); // C=3
+
+    removeRow(arr, 1);          // delete middle (B=2) -> rows [A=1, C=3]
+    const newGroup = addRow(arr, 2); // add new empty row -> [A=1, C=3, new]
+    bindComponentToRow(newGroup.group[0] as any);
+
+    comp.openDropdown(fakeRef);
+    tick();
+
+    // A(1) and C(3) are still used in other rows => must be disabled. B(2) is free.
+    expect(comp.isOptionDisabled({ value: 1 })).withContext('A=1 still used -> disabled').toBeTruthy();
+    expect(comp.isOptionDisabled({ value: 3 })).withContext('C=3 still used -> disabled').toBeTruthy();
+    expect(comp.isOptionDisabled({ value: 2 })).withContext('B=2 removed -> free').toBeFalsy();
+  }));
+
+  it('ISSUE 1b: sibling stored as FormFieldMetadataValueObject (server round-trip shape) must be detected', fakeAsync(() => {
+    const arr = buildArray(2);
+    // Plain (non-authority) vocabulary value after a server round-trip.
+    (arr.get(0).group[0] as any).value = new FormFieldMetadataValueObject('one', null, null, 'one');
+    bindComponentToRow(arr.get(1).group[0] as any);
+    comp.openDropdown(fakeRef);
+    tick();
+    expect(comp.usedSiblingValues.has('one')).withContext('FFMVO.value=one collected').toBeTruthy();
+    expect(comp.isOptionDisabled({ value: 'one' })).withContext('option one disabled').toBeTruthy();
+  }));
+
+  it('ISSUE 1e: authority-controlled duplicate IS detected via authority even when the display value differs', fakeAsync(() => {
+    const arr = buildArray(2);
+    // Sibling as it looks after a server round-trip for an authority vocabulary (Funder):
+    // short value 'NSF' with an authority key.
+    (arr.get(0).group[0] as any).value = new FormFieldMetadataValueObject('NSF', null, 'auth-1', 'NSF');
+    bindComponentToRow(arr.get(1).group[0] as any);
+    comp.openDropdown(fakeRef);
+    tick();
+    // The freshly-loaded option for the SAME funder (authority 'auth-1') whose value is
+    // rendered as the full name. Same funder -> must be treated as a duplicate.
+    const sameFunder = Object.assign(new VocabularyEntry(), {
+      authority: 'auth-1', value: 'National Science Foundation', display: 'National Science Foundation',
+    });
+    expect(comp.isOptionDisabled(sameFunder))
+      .withContext('same authority => same funder => must be disabled (dedup ignores authority)').toBeTruthy();
+  }));
+
+  it('ISSUE 1d: a value chosen by a sibling AFTER open is still blocked at commit (live re-check)', fakeAsync(() => {
+    const arr = buildArray(2);
+    (arr.get(0).group[0] as any).value = entry(1);
+    const rowModel = arr.get(1).group[0] as any;
+    bindComponentToRow(rowModel);
+    comp.openDropdown(fakeRef);
+    tick();
+
+    // A sibling row gains value 2 AFTER this dropdown was opened.
+    const g2 = addRow(arr, 2);
+    (g2.group[0] as any).value = entry(2);
+
+    spyOn(comp.change, 'emit');
+    comp.selectEntry(entry(2), fakeRef); // must refresh live + block
+    expect(comp.change.emit).withContext('duplicate committed via stale set').not.toHaveBeenCalled();
+    expect(rowModel.value).withContext('value must remain unset').toBeUndefined();
+  }));
+
+  it('ISSUE 2: opening the dropdown then blurring (click outside) must NOT clear the selected value', fakeAsync(() => {
+    const arr = buildArray(2);
+    const rowModel = arr.get(0).group[0] as any;
+    bindComponentToRow(rowModel);
+
+    // user has selected value 1 (display 'e1')
+    comp.onSelect(entry(1));
+    tick();
+    let displayed: any;
+    comp.currentValue.subscribe((v) => (displayed = v));
+    expect(rowModel.value).withContext('value selected').toEqual(entry(1));
+    expect(displayed).withContext('display shows selection').toBe('e1');
+
+    // user re-opens the dropdown, then clicks outside (blur) without selecting
+    comp.openDropdown(fakeRef);
+    tick();
+    comp.onBlur(new Event('blur'));
+    tick();
+    comp.currentValue.subscribe((v) => (displayed = v));
+
+    expect(rowModel.value).withContext('value must be preserved after blur').toEqual(entry(1));
+    expect(displayed).withContext('display must be preserved after blur').toBe('e1');
+  }));
+
+  it('GUARD: a disabled option selected via mousedown path is ignored by selectEntry', fakeAsync(() => {
+    const arr = buildArray(2);
+    (arr.get(0).group[0] as any).value = entry(1);
+    const rowModel = arr.get(1).group[0] as any;
+    bindComponentToRow(rowModel);
+    comp.openDropdown(fakeRef);
+    tick();
+    spyOn(comp.change, 'emit');
+    // dsBtnDisabled does NOT block mousedown; selectEntry must guard instead.
+    comp.selectEntry(entry(1), fakeRef);
+    expect(comp.change.emit).withContext('disabled option must not be selected').not.toHaveBeenCalled();
+    expect(rowModel.value).withContext('value untouched').toBeUndefined();
+  }));
+});