unshipped qty cancel during P4205
In E1. 9.1
I have enabled backorder(checked) in all 4 places (P4101/P41026/P41001/Billing Instruction of Both Sold/ship). In SO version processing option commitment tab #1 = BLANK(Bypassing Avl check) and in P4205 (Process tab #3 = 1)
Inventory available 100 EA and sales order qty for 110 EA order created and during P4205 when trying to ship confirm i expected 100 EA will be shipped in line 1 and rest of the 10 EA will be canceled. But P4205 throws error "confirm will cause negative qty"
Is there any setup missing to make the remaning line of 10 EA to cancel during p4205 and 100EA to be shipped?