I don't use the earbuds that came with the IPod, but I can't see that this could be the course of the problem. For I had no playback stops before the latest firmware was installed. And I see that the plug must be drawn out quite a bit before the playback stops, and that this should happen without any impacting force should be completely impossible.
I haven't used the IPod for months now, and this must probably be the reason why it has not yet got any stop now, even though I have played it for maybe an hour or more in order to test it. But as I have experienced before, the stops is starting to occure when I have played it for a while (half an hour or an hour, dependent on how often I use it), and then more and more often until there is no use in trying to play at all.