Synch Outlook tasks for another user

afarr

Our client would like to set a user ABC to sync entries (from NAV to Outlook) for another user XYZ; apparently XYZ reports to ABC. So the filters in Dynamics NAV have
Salesperson Code = FILTER(ABC|XYZ)

With contacts and meetings this has worked well; Outlook has no problem with that.
But with Tasks it gives an error, as listed in the Troubleshooting page http://msdn.microsoft.com/en-us/library/dd983823.aspx : “Task owner can be set to ABC only.”

Why can the owner be set to XYZ for contacts and meetings, but not for tasks?
Is there a way around this?

Thank you.
Alastair