Shadow/Trail Effect when dragging window

When I drag active windows across my screen just say over
other active windows, the window leaves a shadow/trail of
istelf. Sort of like the trail option for the mouse.
And from where I moved the active window it, the screen
is white for a split second and then redraws the
text/active window behind it quite slowly. I do not know
how to fix this problem. This just happened because
before I was able to drag items across the screen without
leaving residue behind it. Any help would be greatly
appreciated. Thank you.