I was under the assumption you could only have max 2 of the same card (1 if legendary) in a deck. In arena, I used this in my favor once to attempt to get a third card so it would re-roll the available cards. However, the second time I did this (can't remember card, costing 0 mana) the third card was inserted into my deck. Thought it might have been a glitch or something. Then later, trying to disenchant Noble Sacrifice (since I had a bunch), when I got down to 3 of them it gave the warning that if I disenchanted I would have fewer than the limit for a deck.
So are there some cards that have limit of 3 per deck??? Has anyone else run into this?
Edit: So I went back and tried again, and it let me disenchant with no message. Then I got the message again the second time I tried to disenchant another card I had 4 of (getting down to 2). Think it might be a logic error in the code. Still, why was I allowed to use 3 of a card in the arena?