Hello Kutay,
Once we save the sales order system update the material requirement in table VBBE or T-code MD04 and when we delete or put reason for rejection in sales order system update VBBE/MD04 and remove the respective sales order from this VBBE/MD04.
Some times system does not update VBBE/MD04 after deleting or putting reason for rejection for sales order due to inconsistency in system. You can execute program SDRQCR21 directly in Production system there is no harm this program just remove the inconsistency in VBBE/MD04.