I've had a few do that, but I believe that I may have weakened the straps by bending them around so the tip of the ground strap was centered over the electrode or even a bit further back. My ground strap were almost verticle, then made a sharper turn towards the electrode. I also tend to run lean, so it could be a combination of what caused it.

If it was "contact", the electrodes would likely have been bent down more.