Are you sure it's not just a garbage collection issue? 
I've had the same problem with Adobe Acrobat until I double-checked the order I was destroying the objects. 
Once I adjusted the order so that it released the objects in the opposite order I instanciated them, the problem went away.

Paul,

I just started using the MM's Drag-and-drop functionality and I only tried the Project Manager Sample Application that comes with the Framework. It would surprise me that Kevin didn't think about that but I'll check this out.

Do you mean you used MM's Drag-and-drop functionality without this error?

Mark