Kinematic-loop examples fails to simplify properly

[baggepinnen]

This example simplifies to a system with rotation-matrix variables
https://github.com/JuliaComputing/Multibody.jl/blob/main/docs/src/examples/kinematic_loops.md?plain=1#L78

julia> ssys
Model fourbar:
Equations (10):
  10 standard: see equations(fourbar)
Unknowns (10): see unknowns(fourbar)
  j1₊phi(t): Relative rotation angle from frame_a to frame_b
  j2₊phi(t): Relative rotation angle from frame_a to frame_b
  j3₊frame_a₊R₁ˏ₁(t)
  j3₊frame_a₊R₂ˏ₂(t)
  j4₊frame_a₊R₂ˏ₁(t)
  j4₊frame_a₊R₁ˏ₂(t)
  j5₊phi(t): Relative rotation angle from frame_a to frame_b
  j3₊phi(t): Relative rotation angle from frame_a to frame_b
  j3₊w(t): angular velocity (rad/s)
  j5₊w(t): angular velocity (rad/s)

[baggepinnen]

This as well https://juliacomputing.github.io/Multibody.jl/dev/examples/spherical_pendulum/

[baggepinnen]

This is a model of a free-falling body, it should simplify to 12 differential equations, but I get three extra algebraic equations

using Multibody
using ModelingToolkit
using Plots
# using JuliaSimCompiler
using OrdinaryDiffEq

t = Multibody.t
D = Differential(t)
world = Multibody.world

@named freeMotion = FreeMotion(state = true, isroot = true)
@named body = Body(m = 1)

eqs = [connect(world.frame_b, freeMotion.frame_a)
       connect(freeMotion.frame_b, body.frame_a)]

@named model = System(eqs, t,
                         systems = [world;
                                    freeMotion;
                                    body])
ssys = multibody(model)