Many people user MS outlook configuration to request read receipts of every email. An issue is observed for the users who use this configurations. Although emails requesting read receipts are read the notification is sent out that the email was deleted without reading.
Indeed, this is an extremely critical bug in Microsoft Exchange 2010 SP1 RU3 V2. To fix this problem you must request a non publically available hotfix KB2471964 from MS PSS by calling them.
This is supposed to be fixed in next release of Exchange Server 2010 SP1 update.