The question arises from a issue in a game between me and Borg. How I always considered these cards:
Altar of Infernia: "All creatures
lose and cannot gain melee +X traits."
Bear strength gives melee +2 to the creature. In theory, you'd have to add 2 melee +1 tokens on the creature to indicate the extra strength. Of course, nobody ever does this since bear strength itself is enough of a reminder and this makes things messy. Altar of infernia would thus remove the 2 melee +1 tokens on the creature but it would not destroy the bear strength itself. Once the altar is destroyed the bear strength gives those melee +2 tokens again.
Ehren gains the tokens, and loses them when the altar is cast. However, when the altar is destroyed, he still lost the tokens.
again, I think an official answer is needed here.