SD billing with excise duty

Hi All

I am creating SD billing for factory sale (pricing procedure JINFAC), which is involved excise duty as well.

VF01 is creating two doc , one for Billing document and one for Excise JV (as we opted Excise invoice during billing).

The issue is in Billing document is creating below entry--

Customer A/c- DR 120 (SO value with excise)

Sales A/c CR 100 (bill value)

Excise Duty A/c CR 20 (excise duty)

And Excise invoice further creating below document

Cenvat suspense A/c DR 20

Excise duty A/c CR 20

Her you can notice excise amount of 20 is credted twice. Can anyone suggest why this is happening. Actually , billing doc should only for 100 and 120.

Regards

Mukta