Contracted vendor defaulting into R/3 requisition even if changed in SRM

Hi

We maintain contracts in R/3 against material groups which are then checked by the system when raising free-text 'describe requirement' shopping carts.

If a material group / product category has contracts with only a single vendor, then this vendor will default in to the shopping cart. The user can, however, change this vendor if they wish.

The problem is when the cart is transferred to R/3 the requisition is generated with the original contract vendor in the 'fixed vendor' field. The vendor the user selected for the shopping cart correctly appears in the 'desired vendor' field.

Is there a way of preventing the contracted vendor appearing in the R/3 requisition when the user has changed it in the SRM shopping cart?

Thanks

David