iSupplier invoice creation

We have migrated from 11i to 12.1.3.  Users are facing a problem in iSupplier portal:

When creating an invoice for a blanket release purchase order in iSupplier portal, invoice type is defaulting into ’Credit Memo’ instead of ’Invoice’.

Is there a way to change this into ’Invoice’ like normal purchase orders?

I have tried personalization but it does not change.  It does not make any sense why blanket po invoice type is defaulted into 'Credit Memo'

Thank you

Senthil