by Ken Task.
In the server where it's not working as expected, go to LDAP settings:
http://yoursite/admin/auth_config.php?auth=ldap
There is a box for page size value. Default value is 250. Comment next to it says:
"Make sure this value is smaller than your LDAP server result set size limit (the maximum number of entries that can be returned in a single query)"
which also suggest there is a setting in LDAP server itself for page size.
'spirit of sharing', Ken