I was in the middle of creating a spell at the altar and I had to leave for a while to collect some slime gel, and when I came back there was an enormous crater where the altar used to be.
So, yeah, what the Hell? I mean, I'm aware that Ars Magica 2 machines can explode if they're given too much power, but the altar wasn't receiving ANY power. So what the actual f**k?! Are these things just designed to self-destruct for no reason or something?