I have one more way to reproduce the same issue:
1. Open some image (or new image).
2. Rectangle Select and mark some area on canvas.
3. Click Undo from toolbar and blue squares remains visible on canvas.
If now picture is saved this blue squares remains in image.
I have one more way to reproduce the same issue:
1. Open some image (or new image).
2. Rectangle Select and mark some area on canvas.
3. Click Undo from toolbar and blue squares remains visible on canvas.
If now picture is saved this blue squares remains in image.
P.S. The same problem with Ellipse Select object.