With a file that I have (I will not release it publicly, not in here), there does not seem to be any undo available with a .kra file. That's all the description of the bug. Even though undo seems to be available, it seems that undo does absolutely nothing at all with a file.
Forgot additional information, Nightly Build of Krita - git 82cfd3e ; OS: MS Windows x10 64-Bit
Since, I can't edit. I have one more issue. Even if undo works, the undo is broken in that file.
Please update your checkout. Lieroz' 572b2ad2868b87a45297563db17fb9e3c98c52f5 commit should have fixed undo.
Right now, I don't have access to that as I can't compile on Windows, and the one on Jenkins is the one I reported the bug with.
Now that the Jenkins checkout has been updated, and I tested it, I believe it works very well. No bugs on undo whatsoever.
Cool! Lieroz is doing such awesome low-level stuff that things like this are to be expected -- so keep on testing master!