While moving or rezising windows ( not opaque mode , but only with frame outline ) all gfx output is frozen, like on AmigaOS :-) I think this even causes xmms to stop playing , because it tries to update the time-position. Happens with other windowmanagers too. ( But not on IRIX 5.3 , so I don't see why it must block on linux )
Cannot reproduce. It is possible that on a very slow system, moving the window around would use up all the CPU time.
The enlightenment window manager ( and some others too , like the CDE WM ) blocks all gfx while the outline of the window is visible, while moving or resizing it. Note that the moving-mode is outline/boxed/... so that only the a single box is dragged and the window appears at the new position when the mouse button is released ( as opposed to opaque moving , when the window is moved/resized in real-time as the mouse is moved ). Whether this is a bug or just a compromise between speed and functionality is a matter of opinion. The 4Dwm ( from IRIX ) does not block gfx , tested with the same X server, but the outline flickers, they must have some special support in the SGI X server.