Unity4.6.0 iOS8.1 landscape left, the buttons in the right side are not available

I have created new project in 4.6.0 and attached this script to camera object:

 void OnGUI() {
     if (GUI.Button (new Rect (Screen.width - 160, 10, 150, 100), "portrait")) {
         Screen.orientation = ScreenOrientation.Portrait;
         Screen.autorotateToLandscapeLeft = false;
         Screen.autorotateToLandscapeRight = false;
         Screen.autorotateToPortrait = false;
         Screen.autorotateToPortraitUpsideDown = false;
     }

     if (GUI.Button (new Rect (Screen.width - 160, 160, 150, 100), "landscape")) {
         Screen.orientation = ScreenOrientation.LandscapeLeft;
         Screen.autorotateToLandscapeLeft = false;
         Screen.autorotateToLandscapeRight = false;
         Screen.autorotateToPortrait = false;
         Screen.autorotateToPortraitUpsideDown = false;
     }

     if (GUI.Button (new Rect (Screen.width - 160, 310, 150, 100), "auto")) {
         Screen.orientation = ScreenOrientation.AutoRotation;
         Screen.autorotateToLandscapeLeft = true;
         Screen.autorotateToLandscapeRight = true;
         Screen.autorotateToPortrait = true;
         Screen.autorotateToPortraitUpsideDown = true;
     }
 }

When I click the "landscape" button in the portrait mode, the orientation becomes landscape left. Then I want to click the "portrait" button, but now the three buttons are available.

Are there some errors in the script?

Thank you very much!