Yeah, it’s not super. It’s a new feature, so I’m just glad it kinda-sorta works for now!
For now you can visit the interrupted file if it lets you, then choose not to save it and quit MyPaint normally. If it doesn’t let you, it should allow you to open the cache folder with your file browser, and have a clear-out.
I’ve bumped up the following bug onto the roadmap for 1.3.0, and I hope somebody’ll pick it up to work on! It’s “just a few buttons” after all…
Okay the newest Git Version of MyPaint has a discard option and checkmark for enable at startup. That should make the recovery much more manageable to work with. Will be available in Version 1.3.