When I copy and paste multiple things from one mockup to another, and then hit ctrl+z to undo it, the Properties Panel no longer works correctly (along with some other weirdness). This happens to me a lot. The only way to recover is to close the application and reopen.
Thank you for your report. I see what you mean.
Redo increases the weirdness. We’ll fix it!
The issue is fixed in 999.23