In EBS R12.3 a Credit Memo Opens a Closed PO, why?

I'm getting a question from Central Procurement  -  why does a credit memo against a closed PO open the lines.  I've tried to tell them it standard functionality but they want more detail.  Does anyone know of an Oracle note or document that explains the idea behind this that is more explanatory for them?  My research tells me it is so the Credit Memo can be processed and opens the lines so the requisitioner can make a return but they are not satisfied with the logic.  Any help would be greatly appreciated.

Patti O