I solved this problem in another way. I noticed that video resumes after clicking Play button twice, so I used DispatcherTimer to call MyPlayer.Play() for one more time a moment later
DispatcherTimer dt = new DispatcherTimer();
public MainPage()
{
InitializeComponent();
dt.Interval = new TimeSpan(0, 0, 0, 1);
dt.Tick += new EventHandler(Ticked);
}
private void Ticked(object sender, EventArgs e)
{
MyPlayer.Play();
dt.Stop();
}
private void Button_Click_1(object sender, RoutedEventArgs e)
{
MyPlayer.Play();
dt.Start();
}