I've tested the animated hazards fairly thoroughly. They're not perfect, but they really can't be. If you hit either one from the left, right, o above, the damage knocks you away from it. If they hit while you are standing, running, or in the air, they pass quickly enough that you don't really get stuck, although you can sorta "climb" the falling rocks a bit before getting thrown out. Accidental climbing isn't unusual, but players are almost never stuck longer than the invincibility period after the initial damage.

The only way to really get stuck is to be standing on the ground, and then jump right as they hit, so that you sink into the ground. The window for this to happen is very small, so you'd almost have to do it on purpose. None of my four play-testers have ever had this happen to them, and they haven't been told about it, so they weren't intentionally trying not to get stuck. I myself have had it happen very rarely, and only once was it not deliberate. Since the problem almost never shows itself and the effect is really cool, I think this is an acceptable flaw. It isn't really much buggier than a lot of the things included by the original developers.

Good observation though.