If the "display content of windows when moving" preference is disabled, and the "wrap workspaces when dragging a window off the screen" preference is enabled, repainting does not occur properly when dragging a window off the screen (onto another workspace). 1) The window being dragged does not disappear after switching into the next workspace, covering screen area that could be used to determine where the window should go. 2) Any windows in the NEW workspace are not filled in, but simply appear as gray rectangles, until the mouse button is released, at which point they are filled in. 3) Any windows in the OLD workspace that are not the window being dragged do not disappear when the workspace switches, but are simply filled with gray, until the mouse button is released, at which point they disappear.
This is similar to #2239, if you don't display the content, then the frame is drawn using XOR directly on screen (this is for very old hardware tha cannot handle moving window in real time) and thus the display needs to be grabbed or the XOR operation can leave artifacts on screen. That's why apps cannot repaint themselves, and this is not avoidable.