The problem is that every now and then, the undo keyboard shortcut just stops working. I close and restart ZBrush and it often fixes it. I haven’t noticed anything I do which could start the problem, such as a change of settings or the CAPS lock being on – it just seems to happen…
This is something I’ve mentioned previously, but I haven’t managed to figure out what could be causing it… I’ve seen one or two posts about the same issue elsewhere, but nobody has given a proper answer to it yet, so I thought I’d bring it up again as I still get this quite often. Other shortcuts might be affected, but for the time being I’ve only noticed it with the undo command.