What can make the Framerate drop while CPU is not roofing in Silverlight?

We have implemented a drag and drop feature that shows a nice simple representation of what we are dragging.

The drag and drop happens on a view that has a lot of elements While dragging, the CPU doesn't go to the roof it stays steady below 10 no matter how long or how fast you try to drag the item, but the framerate drops dramatically from above 60 to less than 10.

EnableRe开发者_运维知识库draw clearly shows that only the item we drag is being redrawn, not the entire page.

How can I find out what is causing that performance issue?

We are using the telerik dragdropmanager, and while dragging, the component is raising events to check if you can drop through 100 elements deep. Solution, until they make that configurable (or that you modify it yourself if you have the source code) is to set IsHitTestVisible to false on heavy elements when you start dragging.

this worked for us :). Dragging is very fluid, even on pages with a lot of elements