Hello,
I have the exact same problem. When I hit any of the menus, they are empty and after a few more seconds, LO shuts down.
I also run LO on Ubuntu 12.10 and have installed LO via a ppa. The problem occurred after I got an update from 4.0.2 to 4.0.3. I have tried to delete the registrymodification file mentioned above to no avail. I have also tried to delete the libreoffice folder in the .config folder, equally without success. I saw that there have been similar problems with 12.04 and that there has been a patch for 12.04, but not for 12.10. See:
Note, that this occurs in connection with Unity. Under gnome I don’t have any problems. Then the menus are displayed correctly and I can choose from them without LO closing down.
Upgrading to 13.04 is not an option for me because of the newly shortened support cycle for non-LTS-versions.