We have a workflow with some template part file that is inserted and edited in context of an assembly to shape it.
I have been able to reproduce it with empty templates.

Create an empty part1.SLDPRT

Create an empty Assem1.SLDASM

From the assy tab insert a component, select part1 and check "Make Virtual", click the PIN mark in the top of the property manager so the command will be repeated.

Click on the