I have a client that uses Exchange 2003 on SBS. Most of the clients are Outlook 2003 and there is no issue with them. However, I have upgraded 2 of the clients to Outlook 2010 and I have an issue with both of them.
If they receive a meeting request for some time in the future, say next Thursday at 10 am, the calendar blocks out all the time from when the request was received until the end of the meeting next week.
This seems to happen no matter who sends the request.