wrong release strategy triggered in PO

Hi SAP Gurus,

Here is the problem:

we have found an old PO where the total value is 102,000 KES but the strategy triggred is <80,000 KES.

Things which we have found out on analysis was:

1) Customer has made PO first , then did GR and then gone back to PO and change the price. Then the Invoice was done.

2) Versions tab in the header data shows the value change.

3) Output of the PO had already been taken before the change of value in PO.

The thing which I can't understand is why was the next release strategy not triggered when the user saved the PO after changing the value.

Kindly help me with this,

Many thanks

Rahul