Adding Approved Suppliers While creating RFQ

 Hi,

I have a small doubt in the creation of RFQ.

I had created one Approved Supplier list for an item as well as those suppliers are also added in a Supplier List.

While i am creating an RFQ, i added all the suppliers by selecting the created Supplier List.

But here is the problem.

Instead of those approved Suppliers of that item, i can also add unapproved suppliers to the RFQ.

I also enabled the attribute 'Use Approved Supplier' for that item.

But i am able to add the unapproved suppliers . 

How can we restrict the unapproved suppliers adding in the RFQ against the approved supplier list.