Actually the main thing is the material GR inspection.
When you change the GR inspection in material master after creating PO, then its not effecting the PO.
You have to re-fetch the material details from material master in PO.
Just try once, Remove the material master from PO-existing line item. Then press enter. System will ask for material number.
Then again enter the material number in line item ans then press enter.
Then check.