I ran into this issue on an Exchange 2010 SP1 with a few users, but not all across the board.

After troubleshooting it down, I found that the common link was users that were migrated from the previous 2003 Exchange farm.

Cleaning the Outlook rules was the first logical step, but it didn't fix the problem then I went through and checked the MAPI connections using MFCMAPI (<a title="MFCMAPI" href="http://mfcmapi.codeplex.com/" target="_blank">link here</a>).  When I checked the rules, the Out of Office wasn't there, even though it had been set in Outlook and OWA.

To fix the issue, finally, I had to clean the Databases that the users that were migrated 2003 were located on.  It appears that there was some MAPI corruption that migrated over with the users.

To clean the database, run the following command in Exchange Powershell:

<!-- p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; line-height: 22.0px; font: 15.0px Calibri; color: #333233} -->New-MailboxRepairRequest  –Database “Database name”  -CorruptionType  SearchFolder, AggregateCounts, ProvisionedFolder, FolderView

Good Luck!