FICA Down Payment getting cleared against ISU Invoicing

Dear Team,

We are getting issue while doing ISU invoicing, which is getting cleared down payment items laying in customer accounts along with invoicing.

Even though the down payment items have clearing restriction "W" which can be cleared through account maintenance but still we are facing the issue.

We have also check the main and sub transaction for down payment which are not maintained in item selection for clearing.

What could be the reason can any one through some light on this.

Thanks & Regards,

Narendra