Good to hear from you again but sorry for the snag! Looks like a weird one.
I couldn’t seem to reproduce the issue on my end (tried on Win 7, Win 10 and OS X El Capitan). I think you do, but would you mind checking that you are running the latest version 3.3.3? You can grab it here if needed: https://balsamiq.com/download
Are you seeing the same issue if you create a new project? If not, would you mind sharing your BMPR file with us so that we can try to reproduce the issue here? As always, we’ll keep your data in the strictest confidence and only long enough to try to debug your issue.
Also, would you mind detailing on your configuration (OS mainly) so I can try reproducing this one with the same configuration you are using?
Sorry again for the hassle with this one, we’ll do our best to help with it!