Got the same thing here. (If) the top menu appears, the menu will work normally for some time, then it will become totally unresponsive and LO will not even react to keyboard-shortcuts. Things like 'Recent Files' will open the wrong files, when you click on one LO will open an other.
Under 12.04 LO was reasonably workable, but under 12.10 it's almost unworkable. (BTW: I use LO Calc most of the time).
I really hope this will get solved, or is it time to look for another distro than Ubuntu? (Or is this a LO problem?)