I kind of made an expression pedal using a cheap volume pedal for my M5, using a 10 pot I think. Anyway, that's beside the point. I think I wired it backwards to what an M5 usually expects, which isn't an issue if you're programming it anyway, a backwards wah is easily fixed etc. I have an issue whereby if the expression pedal isn't in heel position when I start up, the whammy settings go crazy and never go to where they should on toe position. It might be the same issue for other people, but the other way around. Try always powering up at toe position.