Outlook Subject Line being changed automatically

Hi, I have a very strange problem.

Every one and then, apparently Ramdomly, I will receive an email with the
subject "Inbox". I have verified that not only is the sender (lots of
different senders) using a 'proper' subject line but others who receive the
email are also receiving the proper subject. I have no rules set up which
would even come close to changing the subject line. I am using Outlook2k3
running with Exchange 2k3. I've noticed that in my OWA the subject line is
still "inbox" and I also tried checking my mail using an Outlook 2k2 client,
still the same :|

Anyone got any ideas??

Thanks
-Phil