Shift-Insert is bound to the EditPaste command. Deleting this assignment doesn't change the unintended behavior. Ctrl-V is also bound but works correctly. Ctrl-Shift-V was bound to something like EditInsertFile and it worked correctly. Did a bunch of fiddling with keyboard shortcuts with no affect.
Turned off/exited any other app that could impact the keyboard/macros/clipboard and no change. Also, this incorrect behavior happens in no other apps and when uninstalling 9.6.0 and reinstalling 9.5, the correct behavior re-appears for tp. So... seems to point to 9.6 specifically.
It's also weird interaction, in that the clipboard is appended to instead of replaced with a new "copy" command. Which leads me to think it's a bug in the new "duplicate" code (if for no other reason that's it's right next to it in the menu dropdown
in 9.6.0 but I suppose it could be in 9.5.1 or 9.5.2 but I missed those...