Why did Unity 4.5 break my game?

I had a fine little runner/platformer game that was working great! Then I updated to Unity 4.5 and all my colliders are fickle, and my translations are accelerating for no reason when interacting with other triggers that previously didn't effect them. Can someone please explain to me what has happened? I read though most of the release notes, and new features and I can't deduce the cause.

Help is much appreciated.