Drop ship order repricing for partial fulfillment

A drop ship line (order qty = 300) is partially fulfilled by vendor,  the order line shows qty shipped = 100, qty cancelled = 200. This is all on the same line, no split as with a regular order. It also seems to be repricing at this point which we do not want.  We want to charge the customer the original price that existed based on order date.  How do we turn off repricing for this sitiuation?