Incorrect extended amount when changing the quantity in PO receipts

We have just upgraded to E91 and PO receipts seem to work differently from in our old version (B7334). In the old one, if you amended the quantity at the point of receipt you got an error if you did not also amend (or delete and let it re-calculate) the extended amount. In this version, it lets you receive a different quantity at the full value of the originally ordered quantity....no error or warning or anything. I have searched the Processing Options but cannot find anything relevant. Do you REALLY have to rely on users to remember to change it??