Image A Bleeds Into Image B After Edit Copy/Paste — Persists Until Full Develop Reset

As the title suggests.

It happens when I am copy pasting an edit onto another image.
For whatever reason, two images suddenly merge with each other, and I am unable to undo it without reseting the entire image and undoing all my work.
No, it does not undo itself when I close and open the application.

It has happened twice now.