Undo and redo seem to be totally broken in the current version. I installed today's patch and my version is now IntelliJ IDEA (Nika.1) IU-114.243 and all of a sudden undo was just totally hosed. I took a line, entered a space into the middle of a word, and when I hit undo, the line I changed remained as it was and a new line was added containing part of another line somewhere else.
Related to this as I was trying to get my file back to a usable state I ran a diff (I use Perforce) of the file and at one point it showed no differences, yet there was clearly an error (space in the middle of a function name) in the local file.
After a couple restarts the behavior went away and now I cannot get it to happen again, so I cannot right now, give you a set of reproducible steps, however, I thought this issue serious enough that I should at least throw it out there in case one of your dev's might know of a change somewhere that could cause an issue such as this.
I will update this issue if/when I figure out the set of steps to reproduce the issue.