Good to know.
I agree this is a welcome benefit of the native Cinema4D workflow.
I had foreseen to provide some selection tools within the PolyDup tool (loop, fill, ...) but as these are already natively available I haven't been focusing on them just yet. And maybe I won't at all, as it seems a waste of time to implement what is already available.
The console mentions "different point count is not yet implemented". As such, I haven't spend time trying to block this just yet. Implementation will be expanded in future beta(s) ...
I have only been able to reproduce this when I use the shortcut key "c" while the mouse pointer is inside the viewport.
If I use the mouse pointer to select the "make editable" icon then all is fine.
I will provide a fix for this in a next beta.
Thanks for taking the time to test and report. It is much appreciated!