Fields blocked at ME21N

Hello All!

At transaction ME21N, when I put an specific Order Type (Purchasing), two fields (Outline Agreement - MEPO1211-KONNR and outline agreement item - MEPO1211-KTPNR) appears blocked to input information. It appears only for a specific Order type (ZSE).

Anybody knows if those fields can be oppened by an user-exit or badi? or it's a functional customization?

Regards

Ricardo