SSS Problem

Here’s my problem. I am using subsurf scattering in an animation and many of the frames are like the included image. The render time is a lot longer with these frames. I figured out a workaround where I move the sss object very slightly in that frame and then it is fine in that particular frame, and I just replace it in blender’s video editor afterwords.

What is the problem here? Is it my fault? Or is it just a bug? How can I fix it once and for all?
http://i14.photobucket.com/albums/a329/zimbloggy/bad.jpg

Here’s a good frame for comparison
http://i14.photobucket.com/albums/a329/zimbloggy/good.jpg