Hi,
We had same requirement and found that copy control is not touched in DP91/DP90.
We also found note http://service.sap.com/sap/support/notes/554013
which says this is standard system reponse. This note is recorded as invalid for our version but the latest DIP documentation also says items will not be touched in copy control here.
Quote from Introduction DIP 2.1:
"
The only thing to mention is that no customizing for the copy of sales document items must be done, because the system copies only the sales document header to the new sales document type. From the item of the originaldocument, only the account assignment is copied to the new items.
"
Only solution is to use user exit