The DynamicLayerInfo object allows you to set scale ranges for your dynamic layers. When the map control makes MapServer/export requests it does not honour the scale range and submits all the dynamic layers to the endpoint. The 10.1 REST API is not aware of scale ranges on dynamic layers by design (see this thread). This means that all dynamic layers render at all scales.
Is it by design that the Silverlight API does not respect DynamicLayerInfo scale ranges, or is this a bug?