I suppose you just have to keep track of which cards/events have lost-track of which other cards...
I'm pretty sure
all abilities lose track of a card when it moves except the ability that actually moved it. When a card is covered,
all abilities lose track of it. (You can say that the second rule follows from the first because the card moved when it was covered, in the sense that it no longer has the position it had on the top of the pile. No ability moved it though, so that's why no ability still has track of it.)
Welllll, if you discard a Faithful Hound and four Coppers, technically you then have to search through your discard pile to retrieve the Hound and set it aside. So it's not like there's nothing in the game that implicitly makes you do that anyway.
Yeah, Tunnel and Faithful Hound are messed up. I think it was said back in Tunnel discussions that “when you discard this” really ends up needing to be played as “as you are discarding this.”
The reason Tunnel works, is that you're not
moving the Tunnels, you're
revealing them. So in this case you're allowed to fish them out of your discard pile, which is what you're
technically doing if you discarded several cards and then revealing one or several Tunnels (even though IRL you're revealing them as you're discarding).
Of course this means that the rules about fishing out cards from the discard pile are confusing. You're allowed to do it when you're revealing Tunnels, but not when Summoning a Death Cart. It also tells us that the basis for this rule is not the fact that you can't look through your discard pile, as people have suggested. If you know where a card is and an ability allows you to look at or reveal it, you're allowed to do so, even in your discard pile.
People are talking about how it would be if we didn't have that part of the lose-track rule. But note that it doesn't just apply to your discard pile, it also applies to your deck. You can Develop two cards to the top of your deck, and the lower one would be lost track of.
But this makes me wonder how Faithful Hound doesn't break lose-track? Since you're allowed to order the cards when you discard several, you could always put the Hound on top, and then no problem. But if you discard several Hounds, I don't see how you can set aside more than one. Donald?