Unable to delete appointment as a delegate ( delegatewastebasketstyle )

Error description:

While implementing Exchange 2010 SP1 and Microsoft Outlook 2010 I discovered a bug in Outlook. When someone gives delegated access to their calendar, the delegate can add and modify appointments but not delete the appointments. The user receives this error;

Could not complete the deletion. The items may have been already deleted or moved.

Problem description:

A secretary has editor delegated rights to the mailbox of a manager. If the secretary makes an appointment in the calendar of the manager this will succeed. If the secretary wants to change the appointment, this will also succeed. When the secretary want to delete the appointment, the secretary will receive the following error:

Could not complete the deletion. The items may have been already deleted or moved.

This scenario is on a Windows XP system with Microsoft Outlook 2010.

Symptoms:

Deleting the appointment works fine in the following scenarios;

When the same user is logging into Outlook Web App, the user is allowed to delete the same appointment.
When the same user is logging into Microsoft Outlook 2007 on Windows XP, the user is allowed to delete the same appointment.
When the user is allowed to delete the same appointment Microsoft Outlook 2010 on Windows 7 the user is allowed to delete the same appointment.

This is not a rights issue because it works on OWA, Outlook 2007 and on Microsoft Outlook 2010 on Windows 7.
In a default situation, when the secretary deletes the manager's appointment, the deleted appointment will be placed in the deleted items of the secretary.
For some reason - let's say a bug in Outlook 2010 - this does not work.

Actions:

workaround:

The following Knowledge Base article 202517 which describes a workaround for earlier versions of Outlook that we can use in the situation too.

Setting the DelegateWastebasketStyle in HKEY_CURRENT_USER\Software\Microsoft\Office\14.0\Outlook\Options\General can be done with two values:
Setting DelegateWastebasketStyle to 8. Option 8 should arrange that the deleted appointment is moved to the deleted item folder of the delegate. This option is not working for the current situation.
This workaround involves these two actions:

Setting DelegateWastebasketStyle to 4.
OPTIONALLY: Changing the rights on the Deleted Items folder to at least Author. In order to write the deleted item to the other one's "deleted items" folder ( it is possible that the delegate already has this access )

more information:
http://www.msexchangeblog.nl/2011/02/05/unable-to-delete-appointments-as-a-delegate/