BADI not triggered by custom fields

Hello,

I added some custom fields to transaction ME21N via user-exit : function module XM06, screens 101 (header) and 111 (item).

I implemented methods PROCESS_HEADER and PROCESS_ITEM in BADI ME_PROCESS_PO_CUST.

Everything works fine when I'm using the standard fields in the transaction : BADI methods are triggered, user-exit modules are processed, and values from custom fields are caught in both BADI and user-exit.

But when I press "Enter" on my custom fields, these methods aren't triggered. I have to press "Enter" on any other standard field to trigger them. Why ?

Thank you.

Alex.