Clear delivery number during backorder

I would like to backorder a line which has already a delivery number assigned.

Therefore I bring back the status to the pick confirm status and use P4205 and confirm a quantity of zero.

The line gets backordered (last status 904), the pick number is being removed but the delivery number stays.

If I proceed with the process until the new delivery note print (R42535), no new delivery number is being assigned.

Is there a possibility to remove the delivery number during the backorder process or assign a new delivery number?

Thanks,

Janina