Im seeing strange behaviour whilst listing through the limited listing of 1000 groups (we have many more but I cannot list them!)
strange behaviour 1: Next page in the group listing sometimes results in no listings
stange behaviour 2: Page headings says showing xxx to yyyy but in actual fact, shows less.
are you using active directory?
http://www.google.com/search?q=ldap+1000&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla: en-US:official&client=firefox-a
you could also filter your groups so only the ones you want show up, thats what we do. we created chat_dept groups and move people into their respective areas and then have openfire only look at groups that start with chat. also in our AD setup there are lots of groups that are useless to see in openfire (accounts as well).
If you are using AD for your LDAP it has a built in query limit of 1000 results. This can be adjusted by altering the MaxPageSize. The documentation for this is at http://support.microsoft.com/kb/315071.