Recently I've got into some trouble using Ubuntu GNOME OS (16.04), my Ctrl+Z shortcut to undo isn't working at all. It normally does work just fine, so I'm guessing I just broke something but couldn't figure out what exactly. Tried to search on Gnome keyboards configuration, no luck though, there aren't any shortcuts set to Ctrl+Z, also I couldn't find anything on gconf related to that. Others Ctrl hotkeys are working fine, just as Z button is.
Just found it. Was using an extension that had Ctrl+Z attached to it, even though the shortcut was turned off it still took over the default hotkey's behaviour.