I LOVE my M13 - but the one issue that has troubled me from the beginning is programming the expression pedal...sometimes it just behaves a little inconsistently.
The thing that's really busting my balls right now is that there is one scene where I simply cannot get may exp pedal to work at all. It used to work but then one day is just stopped and I can't seem to do anything about it.
Every one of my scenes is set up with a volume pedal and most of them also have a volume controlled compression patch (for boost) and a wah patch. These patches all work fine on all of my scenes except for that one. I've tried copying it over from other scenes in this way: first I test it and see it working, then I copy it to the location I want it and test it again but it doesn't work. It's only in that one scene position. WTH?