Hi,
It look strange. Possible option would be.
1. Hope you would have checked Transport logs & there is no error or warning while movement to QA.
2. Compare the implementation using version comparison in DEV & QA. Make sure both are active.
3. Try to active one more time QA Implementation in QA via SE19.
4. Hope you are doing some changes in PO in ME22N, which should trigger BADI.
Thanks!
Anil Sahni