To reproduce:
1. Create a new project
2. Import a sprite and change the sprite mode to multiple
3. Open sprite editor
4. Make some slices/changes
5. Close the sprite editor - an "Unapplied Import Settings" prompt appears
6. Click on the sprite editor window - the prompt gets hidden behind the window, while everything else remains unclickable. Clicking "Close Tab" from the drop-down box does nothing

The workaround: press alt + f4 to close the sprite editor window
Note: after doing the workaround and closing the prompt - errors are thrown in the console