I don't know about jumping, but on my EX-21 I can hear a change in sound when the blade slips a little in the clamps. It produces a bit of a thump. WHen I stop and flip the tension lever, the blade will bend a bit (because it is loose). Open one clamp, straighten the blade, then close the clamp again and throw the tension lever and you are ready to go again.
Does that sound like what you're seeing?