MediaElement watermark wp8

Hi, I have a game in unity for Android and for iPhone and now i'm porting it to wp8. It's all about full screen movies. I made a test app for this and it works fine (1 button plays one vid another one second vid) but when i copy solution to my project MediaElement starts to act weird. First vid just after splash works fine but last frame freezes and it can be seen like a watermark on menus. The second issue (perhaps conected to first one) is that even if i change the source of vid before 1st lvl it plays the same vid as after splash (looks like it does not change the surce at all). Can anyone tell me what am i doing wrong?

some source here:

 //Unity side
     public void PlayMovie(string filename)
     {
         path = @"video/" + filename;
         try
         {
             Debug.Log("VID: " + VidHasChanged.ToString());
             if (VidHasChanged != null)
             {
                 Debug.Log("I CHANGE TO " + path);
                 VidHasChanged(path);
             }
             else
             {
                 Debug.Log("VID IS NULL");
             }
         }
         catch
         {
             Debug.Log("Something bad happened :(");
         }
     }

 //VS side
 private void OnMediaEnded(object sender, RoutedEventArgs e)
         {
             VideoPlayer.Stop();
             box.Visibility = System.Windows.Visibility.Collapsed;
 
         }
 
 
         private void StartVideo(string path)
         {
             Dispatcher.BeginInvoke(() =>
             {
                 UnityEngine.Debug.Log(VideoPlayer.Source);
                 Uri u = new Uri(path, UriKind.Relative);
                 VideoPlayer.Source = u;
 
 
                 box.Visibility = System.Windows.Visibility.Visible;
                 VideoPlayer.Play();
             });
 
         }
 
 private void Unity_Loaded()
         {
             SetupGeolocator();
             var vScript = UnityEngine.Object.FindObjectOfType<Saver>();
             vScript.VidHasChanged += StartVideo;
         }

and some xaml:

 <DrawingSurfaceBackgroundGrid x:Name="DrawingSurfaceBackground" Loaded="DrawingSurfaceBackground_Loaded">
             <Viewbox x:Name="box" Margin="0" Stretch="Fill" Visibility="Visible">
                 <MediaElement x:Name="VideoPlayer" AutoPlay="True" Height="{Binding PageHeight}" Width="{Binding PageWidth}" MediaEnded="OnMediaEnded" />
             </Viewbox>
         </DrawingSurfaceBackgroundGrid>