I've had my normal eat a couple rats backwards or try, before letting it go and searching out the head.

Considering that the orginal male had the wobble, I don't see how it could be bred out since all spiders descended from him. Wobbles can be just a simple head tilt, or not righting itself immediately when placed on it's back to full on corkscrews.

I am a firm believe that it is always there, no matter how subtle.