I had two different issues, where some effect refered to creatures of specific power and it didn't respect modifications of that power:
1. I had a
Mother of Runes enchanted with an
Empyrial Armor , it was 5/5 at that time. The AI had a
Champion of Lambholt in play. As soon as it had power 2, i couldn't block it anymore (but i could still block with some 2/2 creature).
2. The AI had a
Meekstone in play. I had 4 copies of
Deranged Hermit in play and a lot of squirrels, all of them untapped without any issues.
And then about the issue i reported last week:
leshrac wrote:When i take a mulligan, sometimes i can't see some of my cards, i just get to see the background. Happened three times so far today, and only after a mulligan - two times it was only one card, the other time it was two cards.
This happened very often, and additionally i had at least one occasion where a card in my graveyard was invisible, and another one, where a card in my hand i had already seen became invisible after my drawstep. So there doesn't have to be a direct connection to the mulligan. (But maybe it is already fixed, and i just don't know about that.

)