New files are being placed when selecting with mouse button.
A copy of a subassembly is placed when clicking on it in Pathfinder.
This is a know problem logged in Master PR#9043888 . . .
To resolved this issue you must update to at least ST10 MP11 or SE2019 MP2 for all of the fixes. The Windows update where most users saw improvements because of Windows fixes is 17134.228/version 1803.
For more information on this issue, visit the Solid Edge News Group; here are a few links.