Invitation alerts on Exchange

My iPad2 is set up to use my Exchange account for mail and calendar, and I have the invitation alerts turned on. I am getting some pretty strange invitation alert messages however. Today when I got back to my desk the iPad said I had 262,144 invitations! No, I am not really that popular. In reality, I had 2 new invitations. What's the deal? I've never noticed this behavior on my iPhone4 which is set up to use the same account.