I think I found the problem...
http://damrod.da.funpic.de/SputnikPics/broken_bridge.jpg
http://damrod.da.funpic.de/SputnikPics/broken_bridge_hires.jpg
You can see the broken string below the bridge. On the saddle one can spot some chips, that are actually the profile and shape of the string imprinted into the bridge saddle. It feels kinda rough when going over with your finger.
Calls for a replacement I guess.