Hmm. Well, first of all, I don't know if you meant to imply otherwise, but what "expectedly" means is actually clear. It's if another ability moves the card. Ability x tracks a card, and loses track if any other ability moves it (including the tracked card's own ability of course).
The wrinkle here is that the tracked card doesn't actually have to move while it is being tracked. If it's not where the ability expects to be, for any reason, at any point, the ability loses track. The classic example is when a card is played from the trash. The card's own play ability expects it to be in play. Since it's not, it loses track of the card from the moment it starts tracking it. But it doesn't technically "lose" track, since it never got track in the first place!
And this is actually an important use of the lose-track rule now, since we have Necromancer, Captain, new BoM, new Overlord and new Inheritance (in addtion to TR variants playing a card that trashed itself or moved itself somewhere else).
So is "stop moving" better then? For the reason I said above, I don't think so. But... at first glance you have a point that a card is lost track of because it moves, and then can't move further, so it "stops moving". However! that is, actually, often not the case at all. Let's take a closer look. Let's say Captain plays a Mining Village. The MV's play ability loses track of the MV from the start, even though it has not moved at all! We see that it's the exact same thing for the classic TR + MV. Yes, the MV was trashed earlier, but when MV is played for the second time, it loses track because it's not in play, not because it moved.
So to amend what I said above: To be last track of, the tracked card doesn't actually have to move at all. It only has to not be where the tracking ability expects it to be.