Some quick troubleshooting: If the pedal is not all the way toe-down (but in the middle somewhere) and you press the button twice, does it change presets? I mean that if you are in the middle with the exp pedal, stomping once should restore the default setting that you are currently on, and the second stomp should change to the next preset.

I first had the EV5 as well, it does not work right. If you unplug the EV5, do the presets change normally? I changed to a Moog EP2 and had no further issues.