Eric,
This is currently a product limitation with Dynamic Simulation (DS). Can you create an IdeaStation post asking for this?
The reason is that the motion constraints can be created on anything. They do not need to share a normal or both be cylindrical or even touch to work in the assembly environment. For DS, we are looking at the pitch diameter of the design accelerator gears to know if these are defined correctly. If the design accelerator gear pitch diameters are tangent, DS assumes this is set up correctly and converts the design accelerator motion constraint. When a motion constraint is manually created, DS does not assume your setup is correct and will block automatic joint creation from the assembly motion constraint. We agree this is not ideal. In some cases the setup by users are not correct so, to be conservative, we have blocked this.
Let us know if you have any other issues.
Thanks,
Andy