Copy tree replaces parts in assembly (like save-as would)?

I copied some parts/drawings I was making iterations of with copy-tree. The parts were open in an assembly when I executed copy-tree. Afterwards, I returned to the assembly, inserted my new (modified) part and found that the part that I copied was replaced with the new part, but strangely was still showing the old geometry (which I changed before returning to assembly).  So now I had 2 parts in the tree with the same name which had different geometry.

Do I need to close open instances of the parts that I copy, or is there an option I'm overlooking in Copy Tree?

SW 2015 SP5 - PDM 2015

SolidworksGeneral