Hi Alabo,
I also have OC 8, then 9 insalled on MacOS Server (10.10.5). I also have similar issues, but to get around this (and this has word sucessfully for about 2 years now!) is just to get users to log in with their shortened LDAP username. For example I have Person Ten log in as personten with the persons LDAP password.
That said, I am assuming since you’re on a Mac Server you’re using Open Directory and authenticating against that?
I have also just posted an article on here regarding LDAP login issues…
LDAP User Logging In Issue (Possible Solution) which may and or may not be of any help.