Full load IP & Delta load DTP (BI 7.3)

Hi Experts,

Data flow  of my scenario is source to cube (transactional data).

IP --> full load

Corresponding DTP --> delta load

Data source : 0CO_OM_WBS_7 (WBS Elements: Commitment Line Items)

Here DTP load is functioning as full load & not as delta. So data getting accumulated in the cube after each run, thus resulting in data inconsistency.

I would like to know why DTP delta functionality is not working? Or did I miss something here? Please clarify.