If you open the WPM meter you can freely select from the dropdown list as expected. However, once you start typing and try to change the selection it closes immediately. If you click where the selection would have been if the list hadn't closed then you are still able to select that entry. Closing and reopening the WPM meter seems to be the only way to resolve this behavior.
I'm on Windows 10 with Plover 4.0.0.dev6 and version 0.1.1 of the plugin.
A gif of the issue:

If you open the WPM meter you can freely select from the dropdown list as expected. However, once you start typing and try to change the selection it closes immediately. If you click where the selection would have been if the list hadn't closed then you are still able to select that entry. Closing and reopening the WPM meter seems to be the only way to resolve this behavior.
I'm on Windows 10 with Plover 4.0.0.dev6 and version 0.1.1 of the plugin.
A gif of the issue: