Through experience, my wife, daughter and I have deduced that, unless a player is within about 100 blocks of an unattended minecart, that minecart does not progress, .

We've had situations where a mob has hijacked a cart that we've stepped out of, and we've gone off and left the scene. Later, having gone on with other endeavours, we return to the area in another minecart, only to have a two-minecart collision with that mob, which hadn't moved from the scene until we've returned.

Our previous experiences don't match this, but there has not been a notice to explain that in Save Messages, like where you have things like 'No One Has Ever Seen Junkboy's Face' or 'Always believe that rumours are false, rather than that they are true.'