PO not equal to PR quantity

Dear Expert,

Please help to find the cause of this issue:

I have a PO, from a PR , and this PR with SO.

SO = 1 , PR = 1

and I realized that my PO qty was 2. I wonder why I was able to change the PO since the E warning already set and it's functioning well.

What do you think is the reason why I was able to put the PO Qty greater than PR. In PR, there's no change log that qty was changed, and even in SO.

I tried to simulate again, changing the PO qty greater than PR but I cannot proceed because of the Error warning. So now it's so confusing how this happens, GR and IR already done.

Kindly help.

regards,

zhie