Palette changes that modify the pixels can't be undone

When the image is in "animation" mode, no matter the number of frames, there is 
a bug in the Palette screen that can make the changes non undoable: If you use 
any function that causes a remap (x-inv, x-swap, reduce, sort), the remap is 
performed not only on the current "History" step of all the frames, but also on 
the previous history step of the current frame. Then if you hit Cancel to close 
the window, or if you press OK and immediately Undo, the image appears 
completely corrupted.

This bug was probably present since the "no layers" variant, but it's really 
prominent in 2.4

Original issue reported on code.google.com by yrizoud on 15 Oct 2012 at 6:31

jiayouxjh / grafx2

Palette changes that modify the pixels can't be undone #514