Hi Alessandro,
I have verified that the plugin system's USORG table has the BUKRS value. See screen below. This table looks exactly the same in non-prod, but the issue only exists in GRC Production.
We are in the process of implementing note 1970172, which allegedly corrects the defect with GRAC_PFCG_AUTHORIZATION_SYNC. I will not know if this worked until 4/23/2015, so I will report back then.
Thanks for your efforts, and I hope we can find the solution.
-Ken