Drag with Nested ModalPopupExtender

I am using the ModalPopupExtender in a user control and nesting that user control to create nested modal popups.  Everything works fine with the nesting and the dragging is good on the primary layer of popups but any nested popups shift when I click on their drag handle so that the popup is now some distance down and to the right of the mouse cursor.  Dragging then works as normal but the popup is away from the cursor. Has anyone else experienced this?  Does anyone know of a solution?