Why my GUI.Window is at the wrong location in the Editor?

I try to play with GUI.Window but when I run my application in the Editor, the Windows are at the bad position. I though my code was wrong but when i try to build it as a webplayer or standalone, the windows are well placed. Why ? Is that a known bug ?

Here a example which show a window center on the Screen...

private Rect windowHost = new Rect(Screen.width / 2 - 250, Screen.height / 2 - 250, 500, 500); 

public void OnGUI() 
windowHost = GUI.Window(1, windowHost, HostGame, "Host a Game"); 

public void HostGame(int windowID)
 GUILayout.Label("Host Window");

The problem is that Screen.width and Screen.height don't immediately give the right values during construction of your class (And generally using functions/properties in member variable declarations is a very bad idea, so try not to do that anyway)

If you shift the rect declaration into OnGUI, it should fix it