Question marks created by pressing undo a lot

[ImpJr]

I was drawing in between layers and tried to draw a mushroom but I didn't like how big it was so I hit undo a bunch of times to where I started before it existed when after pressing it a lot, I suddenly had my entire layer deleted and replaced with a huge question mark. When I tried to hit undo and redo, hoping it would fix it, even more question marks appeared on my screen. I looked at the bug reports and nobody else seemed to be having this issue so I'm quite perplexed and don't know what to do. I can still make a new layer and deleted the glitched one but this could be a problem for people who put a lot of work into a layer and then had the entire thing destroyed. I hope this bug can be fixed soon before it becomes an even bigger issue for others.