
Classic BC behavior that catches everyone off guard.
When BC refreshes the PO, it auto-calculates Qty. to Receive = Quantity - Qty. Received for every line. So if you have a line where Quantity = 1 and nothing was received yet, BC silently includes it even if you never touched that field.
Quick fix: Before posting, manually set Qty. to Receive = 0 on every line you don't want included. BC won't skip a line just because it looks blank, it needs an explicit zero.
Also worth checking if warehouse put-away activity touched that order, as that can create quantity commitments that show up as phantom lines in the Item Ledger Entry.