I have a background image on my containing user control that is just a pattern. At times I can see a border around my overlay that shows this background image all the way through the map. I can see the overlay still and all map layers are visible. There is just a box around my overlay that shows the background through the map control. Also, when the hit test fails, this see-through box will be visible in a different location without the content of the overlay. This different location seems to be it's top-left corner being the center of the map control. Another oddity here is that the containing control seems to be a factor. We are using a third party tab control with docking ability. I'm seeing this behavior when it is tabbed but not when it is a floating window using the exact same executable. You can change from tabbed to floating at run-time. Have you guys heard of anything else like this before?