Please help!

We're running Fedora Core 6 PCs that use LDAP for user authentication.
I've noticed a quirk that wasn't present on our previous FC3-based
systems. When a LDAP user is logged into a PC, they do not appear in
the user lists generated by "w", "who" or "users" - only root (me)...

All the LDAP information is coming through fine (home directory,
username, etc all recognised by the system and present in the appropriate
environment variables). Curiously, "who /var/log/wtmp" displays a list
of past logins, so the system is picking them up somewhere along the way...

Any ideas? Although this doesn't effect the users working on the PCs
(everything seems to work fine for them) it does make it difficult to
remotely check if someone is using a PC before running updates, forcing
a shutdown , etc...

Thanks in advance!