The fix was actually missing few bits:
- Firstly, the operator itself is not to do UNDO push
- Secondly, multires sculpt/top level are not pushed to the undo
node, so undo can not happen reliably.
It should be possible to incorporate some of the work from WIP patch
for propagation undo, but it needs more work.
Reverting code base to the previous state, since currently things
are actually a bit more confusing then they used to be.
This reverts commit 0c928087a3.
1222f561a2