We just finished this one up for 9.05 - same might apply for 8.03. You definitely have to $0 out all the costs when you bring in the RMA, you then disposition it to a job. The gotcha we ran into is making sure your product groups match between the sales order and the job. Not sure how far back this bug went but we hit it on 9.05.702a, but the job follows the part master even when tied to sales order demand - and we issue our sales orders for repair (or warranty) and are a standard shop.
If the job follows the same product group as the sales order and we disposition the RMA to the job at $0 then we only transact for the actual cost on the job rather than standard cost.
Jenn