QMediaPlayer: serious error = -1072871856 on setPosition

When playing a mp4 video using a slightly modified version of video widget example to allow loading wmf plugin and the position is changed repeatedly using the slider the example will eventually print out:

handleSessionEvent: serious error = -1072871856

and after the video needs to be reopened once it finishes.

Steps to reproduce the error:

1. start the example
2. load a mp4 video
3. play
4. drag the slider back and forth for a while