Categories and Favourites no longer working

[Lukas Winter]

Since a few days ago the applications menu is just a huge alphabetical list of applications. Clicking on categories such as "Games" or "Internet" does nothing. I don't get a list of the most used programs. Some programs seem absent from the list. Searching for an application in the list works and gives me installable search hits. Files & Folders work as expected.
I can't tell what triggered this behavour. Maybe I installed some packages or have run an update. Unfortunately I cannot even make a screenshot, no dialog appears when I open the applications menu and press Print Screen.

Is there a way to rebuild the application database if something like that exists?