Blanket PO revision gets incremented after updating Amount Agreed value but does not go for Re-Appro

Dear Friends,

We are on Oracle Apps Version: 11.5.10.2 and i am facing the below mentioned problem in Purchasing.

1. For Blanket PO, in header level DFF, we have enabled a segment (mapped to attribute1 column) which can accept either Yes or No value and the default value will be No.

2. We also have a trigger on PO_HEADERS_ALL table, which fires when the segment value is changed to "Yes". This trigger basically updates the Amount Agreed field from NULL to (ordered_qty*unit_price).

3. Initially when we create a Blanket Purchase Agreement, we usually give quanity and unit price and the amount agreed will be NULL