When the moons are in the correct alignment,  October has 5 Sundays,  your running Exchange 2003,  you running in GMT timezone and using an email client using CDO ... you may find time will shift one hour!

Well,  to be honest,  I might have been lying about the 'moon alignment' piece but the rest is true.  It appears that there is a bug in CDO for Exchange 2003 that when you have an October with 5 Sundays,  meetings will not be entered as expected.

Luckily there is a hotfix for Exchange 2003 (also one for Exchange 5.5 and Exchange 2000) out and you have until 2010 before this problem would occur again.  That should give you enough time to ensure that if you dont apply the fix this time that you do for the next time we have a 'month of Sundays'.