@AmigaMance
I believe that CLS2086 was referring to the OS4 implementation, which doesn't have that issue AFAIK.
DRAGON, I imagine, has to create a new screen with a composite of the two dragged screens when a screen is dragged - this might cause the split-second blackness, perhaps? And since you're running on a Classic system, software screen dragging will certainly use up a heck of a lot of CPU power...
Of course, DRAGON can also move screens horizontally which is a completely new feature.
