SAP B1 Approval

Dear Experts,

Please guide me regarding Approvals in SAP B1.

I have set an Approvals on Marketing Documents. User is sending documents for Approvals through copy to option from base document to Target document.

Normally we use to make Target Document from Copy To option. But When we have already forwarded the Target Document from Base Document for Approval then why User is able to send same document for approval again & again.

Thanks'