As the title says, Telling Time reveals the card you put in your hand to your opponent.
This is a really tricky bug, because the only person that would ever know it happened is your opponent, and they would only know they shouldn't have seen the revealed card if they read the card text of Telling Time.
I'm not sure how long this card has been broken, but I noticed it happen a few times, and I finally thought to re-read telling time and see that it should not reveal the card you chose. After that, I confirmed with an opponent each of the cards they put in their hand with Telling Time over the course of the match, it revealed the correct card to me every time.
Now, I suppose this won't affect every match, but I suspect that more than a few people have lost a game recently due to an opponent knowing the card they just drew from Telling Time and playing around it.
I've already reported this one, but until we hear that it's been fixed, be aware of it, because you'd never know anything was wrong if you are the one running the card.