Strange LDAP-behavior

[Stefan]

Hello List!
I'm using kolab 2.0!
When I do:
./ldapsearch -h mykolabserver "(telephonenumber=+49 4711)" mail
I get the my own mail address.

When I do:
./ldapsearch -h mykolabserver "(facsimiletelephonenumber=+49 4712)" mail
No entry is found! I know definitly, that my Fax-nr. is set in LDAP!

Does someone know, how to solv this?
Do I have to create an index first?
TIA
Stefan