It would make sense for that to be the way they fix it, but I just logged into the beta 5 minutes ago and tested it out, and it doesn't seem to have been fixed quite yet. I popped Arcane Power and then proceeded to cast alternating Arcane Barrages and Arcane Missiles at everything in sight. I was critting on average every other cast. At one point, I critted on an Arcane Barrage, then all five missiles of an Arcane Missiles cast in a row. If it isn't Arcane Power causing that, then then I can't explain it.

Still, I fully expect this to be fixed in one way or another, as it really does feel too powerful at the moment. It's a good feeling, though!

And I just tried it some more, and I can see that the Arcane Potency buff does pop up upon casting Arcane Power and then disappear after the next spellcast, though Arcane Power is not consumed, so it would seem this is their fix. The thing is, it still doesn't seem to be lowering my chance to crit. I'm definitely critting more often with Arcane Power up than I am without it. Oh well, that's the beta for you.