Why can't I set currPosition in Windows Media Player Control

Question

I'm using a windows media control (AxWMPLib.AxWindowsMediaPlayer) in a Winforms app to play an mp4 video. I want to be able to start the video at a particular position and then stop playing after a certain number of seconds.

My problem is that when I try to set the current position, it either sets the current position to zero (before it starts to play or when it's paused) or a small number such as 6 (if it's already playing).

This is how I'm trying to change the current position: m_windowsMediaPlayer.Ctlcontrols.currentPosition = value;

This question Embedded Windows Media Player Set Position is slow suggests that the problem could be caused by a low number of key frames, but it doesn't matter whether I try to set it to 30 seconds or 1200 seconds. It still starts playing at 6 seconds again.

This question Windows Media Player control - get/set video position? shows that setting currentPosition works for some people.

Here's the relevant code:

        m_windowsMediaPlayer.URL = GetVideoFileFullPath();
        RestartVideo();

    private void RestartVideo()
    {
        m_windowsMediaPlayer.Ctlcontrols.currentPosition = StartTime;

        StopTimer();
        StartTimer();

        m_windowsMediaPlayer.Ctlcontrols.play();
    }

I also tried adding an OpenStateChanged event since I thought maybe everything was delayed, so I should set it only after the file was truly opened. But that didn't help either.

    private void m_windowsMediaPlayer_OpenStateChange(object sender, AxWMPLib._WMPOCXEvents_OpenStateChangeEvent e)
    {
        if (m_windowsMediaPlayer.playState == WMPLib.WMPPlayState.wmppsPlaying)
        {
            if (m_start)
            {
                m_windowsMediaPlayer.Ctlcontrols.pause();
                m_start=false;
                RestartVideo();
            }
        }
    }

The mp4 file that I'm displaying is still being appended to by another app. But the problem exists with static mp4 files too. If another video format would work better, I should be able to change the other app to use that video format. I looked at using vlcDotNetForms, but since I want to be able to distribute this app with as few external dependencies as possible, I am hoping to solve this by using something that ships with windows.

One other point: I need to support Windows Vista machines on up, and I can't count on them having .NET 3.5 or newer. Currently I'm targeting .NET 2, but I could target .NET 3 if necessary. I'm seeing these problem on Windows 8.1.