According to the SQL Server Manageability Team, there is a bug in the maintenance plan engine that may cause it to delete historical information too soon.
Service Pack 2 includes the ability delete old data using the History Cleanup Task and Maintenance Cleanup Task. These tasks have been changed to allow deleting entries whose age is measured in hours in addition to the days, weeks, months, and years previously supported. Unfortunately a bug in the service pack may cause the time span to be misinterpreted.
No fix is being offered at this time, but the workaround is to simply open each maintenance task and manually reset the interval.
