Undo/Redo unexpected behavior after importing from file

[SquidXTV]

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• [x] I've definitely found a bug (it you're not sure, please use image.sc instead)
• [x] I've checked https://qupath.github.io for a new release that might already have fixed the issue
• [x] I've checked the Changelog to see if the bug has already been fixed in the next release
• [x] I've checked for existing GitHub issues describing the same problem

Bug report

Describe the bug If you import objects from a file, then select an object like a rectangle and change/move it and then finally using undo it weirdly going to delete all added objects instead of undoing the change/move.

To Reproduce Steps to reproduce the behavior:

1. Loading image using Open...
2. Loading objects using Import objects from file
3. Double click (select) any object
4. Move/Change the selected object, like transforming a rectangle or whatever
5. Undoing the action

Expected behavior Undoing the move/change of the object. Instead it just deletes all objects.

Desktop (please complete the following information):

• OS: Windows
• QuPath Version: 0.5.1