5.2 who not showing all login

I have 1 box running 5.2 and another running 5.3. Both use the NIS accounts and NFS home directories. Users can telnet on to both and 'who' displays the login.
However when users run xterms using a remote X server (e.g. Exceed), by telnetting then running
/usr/bin/X11/xterm -d xxx.xxx.xxx.xxx:0

The AIX5.3 box shows the logon with who
somebody pts/13 30 Sep 14:14 (xxx.xxx.xxx.xxx)
and last
somebody pts/13 xxx.xxx.xxx.xxx 30 Sep 14:14 still logged in.

But the AIX5.2 doesn't show the login in who and last outputs
somebody pts/8 xxx.xxx.xxx.xxx 30 Sep 14:14 - 14:14 (00:00)

This means that tools like idled cannot teminate those user session that have been idled for a long time.

I have checked and cleaned up /etc/utmp and /var/adm/wtmp using fwtmp, installed the fis for IY78358, but still no joy.

Any ideas?

Can you post the exact, complete output of the commands you are running?