AP Invoice Hold, Qty Billed > Qty Received Functionality

I've been pouring over the manuals and comparing data elements between two Vendors and their po's. One po went to status Holds = 1 when qty billed was greater than qty rec'd. The other po did not.

Before I start a SR, is there something obvious I could examine comparatively between vendors and po's to maybe find the missing information.

I did find some differences: the vendor/po that was placed on hold had match to PO assigned and there was no qty tolerance in po line detail. The vendor/po that was not held was a match to receipt and had a 10% Warning assigned in po line detail. (however, the qty billed also exceeded 10% tolerance).