This bug is reproducable. Enter the world in fullscreen mode. Open the Overseer window. Press Alt-Return to activate the windowed mode. Screen turns black, EQ mouse cursor is visible and movable. Nothing happens for minutes and the windows taskbar and taskmanager are not accessible just like in a freeze. However it is possible to close the client with an external programm via hotkey. I tried another method and found out that the reason for the black screen was that the Overseer window appeared as being minimized in the windowed mode even that it was maximized in full screen. So the bug is that the state of the Overseer window (max/min) did not get synchronized. The freeze bug for opening a minimized Overseer window is already known and connected with this bug here. Enter the world in fullscreen mode. Press Alt-Return to activate the windowed mode. Open the Overseer window. Back screen again for about one minute. Overseer window appears being minimized. After maximizing the Overseer window in the windowed mode it was possible to switch back and forth with Alt-Return without extreme lag. "Only" 10 seconds lag.
