Ok, so sometimes, when I just made a mistake, I click undo once or twice, depending on how many lines it took to make the mistake and wait a second or two. Then nothing happens so i'm like "Huh?" and, naturally as a blonde, I click it like 10 more times, and nothing happens, I think my computer's frozen, but I start to draw, and for each line I make, it undos something from before the mistake, by the time I've made 10 lines, half the drawing is gone. DOES THIS HAPPEN TO anyone ELSE?!?!? If it does, is there a way to do anything about it, besides just pressing redo 20 times? (for good measure, I press it twice as many times.)
We've had a few reports of people having this problem on the rare occasion. We'll do some testing and try and replicate the problem and address any issues we find.
For now try using the quicksave feature as you go and if you have problems, clear the drawing and load it again and it may fix your undo problem.