Hi Mukthar,
Yes. You are right about sort key.
The problem here is that there is a different content between FB03 and FAGL_FC_VAL about BSEG-ZUONR(asssignment). The content is correct in BSEG and BSIK.
The FAGL_FC_VAL transaction is changing the content of ZUONR field, just to show this field. In true, the content field not was changed in BSEG/BSIK.
Regards,
Valter