Having calendar with Saturday and Sunday closed, and transport days of 2, with the procurement parameter "Supplier requested and confirmed shipment dates" enabled. You create an end customer direct deliver order with requested ship date on a Thursday and Requested receipt date gets calculated on a Monday, what is correct. When the sales line is saved, the intercompany chain is created (IC purchase and IC sales order), the Requested receipt date changes to Sunday.

Reference: Bug 1083197