Does SQL*Loader in direct path mode temporarily set NULLABLE to 'D' but doesn't set it back?

That's just a theory, since

SELECT owner,table_name,column_name,nullable

FROM dba_tab_columns

where nullable = 'D'

 and table_name='OSQ_MAP'

 and column_name='LINE';

but I can't reproduce it no matter what I do. NULLABLE is either "Y" or "N" and I can't find any other possible values. Thanks.