in which case there is value populated in EKKO-ZBDIT and no value in EKKO- ZTERM for UB purchse order

Hi All,

I have two UB documnet type purchase order.

1)  Plant 1 ( supply plant)  -> Plant 2 ( Recieving plant)

there is vendor master  to assign to plant 1 , payment term is  ZX11 in the vendor master  , payment day is 90

2)  Plant 3 ( supply plant) --> PLant 2 ( Recieving plant)

there is vendor master  to assign to plant 3 , payment term is  ZX12 in the vendor master  , payment day is 30

when i created UB documnet type purchase order, for  point 1 , there is value  '90'  in EKKO-ZBDIT,

but for point 2, there is no value in EKKO-ZBDIT.

Actually for UB doucment type PO , we don't want to have vuale in EKKO-ZBDIT.  but i don't know why for point 1 , why system populate value '90' in EKKO-ZBDIT . Could you please let me know the reason ? thanks!