So, R&D has had lengthy discussions about Cavern of Souls. The card's templating is unique; there hasn't ever been a card before that has two invisible effects that have such different implications for the game state, and that wasn't anticipated before release. Given the problems that it causes, I suspect it'll be the last to use this template.
In the end, the original designer intent of the card was that it always applied when you cast a spell with the appropriate type, whether you had actually remembered to activate it properly or not. Because of this, they've asked us to reconsider the ruling that you need to announce Cavern of Souls if you want the spell to be counterable.
We're sympathetic to their desires and, as I said in the previous mail, there were arguments to be made for both sides, even if philosophy supported the original interpretation better. As a result, we're reversing the ruling. If a Cavern of Souls gets tapped for the appropriate creature type, the spell is uncounterable whether they say anything or not. We'd still prefer that players be clear about the game state, of course.
There'll probably be a bunch of confusion about this initially. We did a good job (I think) of getting the word out the first time around, so it'll take a while to educate everyone about the reverse. I'd strongly encourage everyone to make reminder announcements at their events for the next few. I know I will be at the start of GP:Anaheim!
Unique and messy cards are, fortunately, few and far between, and tournament-playable ones are rarer still. Apologies for the confusion, and hopefully this uses up the allocation for the next several years!

109.1 Un objet est une capacité sur la pile, une carte, la copie d’une carte, un jeton, un sort, un permanent ou un emblème.

c'est un mana. A-t'on vraiment besoin de le catégoriser ? Je ne pense pas.