mailtool and procmail (I've read the FAQ!)

Our mailhost is running Solaris 2.4, /var/mail
is a local directory NFS exported to Solaris 2.4
and 2.5 clients with most users using Sun's mailtool.
All mail is delivered on the mailhost (i.e. that's
where procmail runs).

I've read the FAQ and archives of the mailing list
and defined NO_fcntl_LOCK and NO_lockf_LOCK.

"procmail -v" says
Locking strategies:     dotlocking
Default rcfile:         $HOME/.procmailrc
System mailbox:         /usr/mail/$LOGNAME

I still get the "mailtool is confused about the state
of your mailbox" bug. Anybody know what I'm overlooking,
or can I just not use procmail at all - which would be
a shame?

Thanks,
Steve