Heading of custom field in table MARC not shown in SE16N

Hi SAP ABAP Experts,

Hope everyone can advise me some hints or recommend what steps I should perform in this below situation.

I have created a custom field ZZMATSOURCE in table MARC and assigned it in Purchasing view.  When I use SE16N to display table MARC, I can see the value but the heading is not shown properly.

Thanks and regards,

Danny