Ok, I did some more testing and this seems to be related to Cartographer_LookNFeel.
If I turn off the LookNFeel Module, the Zone leve ranges show correctly, If I turn it back on they disappear again. I tried to fiddle with LookNFeels settings (I use a transparency of 0% e.g.) but no chance to get the levels back. I wonder why only some people seem to have this problem...Anyone any ideas?
p.s.: I am using the latest SVN Cartographer packager.