Hi Vei,
The field KNTTP has the Change document enables, this is a standard field.
Have you tried checking the delta, if it is picking if you are performing any changes at other object levels along with account assignment?
case 1: try to change the account assignment along with the other fields and check if delta is captured or not?
Case 2: try to change only the account assignment and check for the entries in CDHDR n CDPOS tables. how the entries are stored.
this needs a functional knowledge to trace out what changes are reflecting in delta n which are not individually or linking to other objects.
Regards
KP