lists won't undo in in the Wysiwyg editor

I’ve come across a bit of a problem with the Wysiwyg editor. I added a list on the page but when I go to undo the list by clicking the button again it doesn’t work. I’ve tried deactivating off the plugins and switching the theme back to twenty ten/twenty eleven, neither worked.
I came across the problem with another site created and just thought it was a problem with 3.3/3.3.1 because on the test server it worked and that one is running version 3.2.1.
I can always pull the ul and li tags out but that doesn’t help the client do it.

Has anyone else came across this problem? Please let me know.

Thanks!