Hi Maria,
This is because of Item category -billing relevance settings
for Debit memo request, item category is L2N which has C as Billing relevance, status according to target quantity
Unless and until you do the Billing for the item, it will not update any status
as I noticed, even if you update Reason for Rejection system allows to create Billing document with Zero value for Debit and credit memo Request and status updated
thanks
santosh