Currently the following sequence of commands:

stage.sizeToScene();
stage.setResizable(false);

causes the stage to acquire an incorrect size (the size the stage had before the sizeToScene call) on glass gtk port. The problem is that to make a window non-resizable on X11, its minimum size and maximum size must be set to the same value. The current implementation uses the last reported size from system, not taking into account, that this size will change eventually by the sizeToScene request.