IK Animation - Some frames break randomly

I’m using IK Animation to animate a character, and everything seems right. If I check all the frames in the animator one by one, the animation moves correctly. But if I run the animation, some frames break and a limb is fliped for no apparent reason.

Here’s a video of what is happening:
link text

As you can see, the animation is running in very slow motion so the broken frame can be easily appreciated. Then, I check all the frames one by one and everything seems right. Does anybody know what is going on here?

If you need more information, please ask :slight_smile:

Note: this happens both in the editor and in the build.