document splitting is not working

Dear SAP friends,

We have implemented ECC 6.0, Document splitting is active at business area level.

In document splitting rule i have made business area is mandatory field, But while posting the document even if i not give the business area also system is posting the document, as i know system should not post the document as business area is not found in any of the line item.

Please let me know in this regard,

Regards,

Anand