field sometimes missing in MM03 and cannot find out where to definition

Hi Experts,

I'm new in ERP and facing a problem that really drive me crazy these days.

There's a bug in our existing z-report, which prepares a BDC session to modify the Material data.

And in the MRP 1 view, the "in-house production" (MARC-DZEIT) field sometimes appears and sometimes is hidden, since I don't know the rule, the BDC session will get error if it is trying to update the field while it's hidden.

I've asked Google and SCN for days and find out some t-codes like OMSA, OMS9 etc. I've go through these transactions and screens and all I can find is as follows:

MARC-DZEIT is configured in Field sel. group 53,

and for Field sel. group 53, I click "Sort Entries..." "by field selection", and I can see there's only one row which value is "Hidden", and the "Field ref." of this row is 'F', I click the "where-used-icon" button to see the detail description, and it shows: "

special usage

The field reference F is referenced in external procurement

"

If I understood that correctly, It seems meaning that the external procurement will make that Field sel. group hidden (since hidden is the top priority), and thus the field MARC-DZEIT will be hidden.

But strange things happens: even some material of which the procurement type is E-In-house production, the MARC-DZEIT field is also missing, is there anyone can help me or explain me why? Many thanks for the answer!!!