Change position of LibVLCSharp media player

Question

I'm using LibVLCSharp.WPF to record and play videos. I have some issue with changing video's position by forward and backwards.

First time click on Play button this method is called:

public void StartPlayback(TimeSpan fromPos, double playbackRate)
{
    _mediaPlayer.SetRate((float)playbackRate);
    SetPosition(fromPos);
    Timer.Start();
    _mediaPlayer.Play();
}

After changing video's position with SetPosition method by given timespan it should be play. This is my method to change position.

public void SetPosition(TimeSpan ts)
{
    TimeSpan absoluteTs = ts;
    if (ts < TimeSpan.Zero)
    {
        absoluteTs = ts.Duration();
    }
    _mediaPlayer.Position = (float)(absoluteTs.TotalMilliseconds / _mediaPlayer.Length);
}

But after changing position video is not playing at all and doesn't change frame. I don't quiet understand what I'm missing here.