Change the tax rate area in a GR

When we raise a PO, we can include a tax rate area or leave it blank.

If we include the tax rate area or we leave it blank, the system doesn´t allow me to modify the tax rate area at the time of the GR.

The system allows me to modify the tax rate area but it will not save it. As soon as the GR is done, I inquiry the GR done and the tax rate area is the same than the tax rate area that we had in the PO.

Thanks,

Cesar