I encountered an issue today where the screen didn't redraw (3d client) after unlocking computer.

This was on Vista 64 bit while using the standalone client.

Repro steps:
1) start standalone (3d) client
2) Lock computer (ctrl-alt-del | Lock this computer)
(For this step you don't even need to lock the computer simply ctrl-alt-del then esc causes the problem)
3) Log back in

Notice that the game window now is completely black. To get the game to redraw the screen you need to resize the game window.

Sometimes when you log back in and redraw the screen to get it to draw again the game will crash when you try and do something like join game, etc.