You can playback more than one GPX file at a time:
- start a gpx playback
- manually move forward the progress bar
- on the map display, select the upper right 'Menu' button
- restart the same gpx playback
- watching the progress bar, you can see it process two positions
- at this point, even if you use the 'Stop' button on the right of the progress bar, the first gpx replay is still running and there is no way of stopping it.