Checked using native ADO.NET query:
select *
from Database.Metadata.Columns@MM_NAARDEN
where owner = 'MARINA'
and table_name = 'MA_BELEG_KOPF'
and datatype = 'DATE'
The column is indeed required and correctly translated into an Invantive SQL table. However, the translation of an invalid date in a required column into a Gregorian has a bug. This will be fixed in the BETA released today.