If you want a look at the code which generates the menu:
https://www.scenology.eu/de/menu.txt
The website with the problem is:
https://www.scenology.eu/de/
If you load that page the first tab says “Kolloquium zur Theorie der Szenografie”, if you click on another tab it changes to “Home” (what it’s supposed to be), same goes for the tab “Referenten”. I always placed the short title, like “Home” in the normal title field of my Page and the long title in a custom field called “title”.
I’m using the K2 theme and WordPress 2.3.1.