Owner Change from nobody to UserID xxx

Situation:
Ticket created (Web) but not assigned to a person (even not to NOBODY).
Same situation when creating Ticket via Mail.

Default queue shows Ticket Owner: nobody

Now assigning this ticket to a person of the staff (Owner change from nobody
to xxx).

The script Owner change does nothing! No mail to xxx.

It works o.k. for a change between person xx1 to person xx2, but not when xx1
is nobody.

I have realized the information of the assigned person too, if the assignment
takes place when creating the ticket.

The problem is: no information of the first assigned person via Mail if
someone forgets to assign the ticket when creating!

Any help appreciated!

Thanks

Michael