Hi Mark. Okay, I’m not near the pedal right now but here are some things to note.
Did you save the preset with the pedal in the correct position (ex: tune the pedal with the toe down)? Is the Boss EV5 knob in the proper position? That’s basic troubleshooting, but I was having the same problem when using the EV5. It was temperamental at best and sometimes I would unplug the ring thing, shut down my power, start back up, make sure the ring thing sounded good on its own, plugged back in the exp pedal, and it still might do exactly as you’re describing, with off-pitch notes. That is, until the next day when it would work properly again. I’m convinced that its the EV5, and returned it and bought a Moog EP2 as mentioned before, but I can’t give a review for about 10 days when I return home from a long trip.

Listening to some used CD grabs from yesterday: Beck’s “Mutations”, The Cult’s “Sonic Temple”, and Ciccone Youth’s “Whitey Album.”

UPDATE. I returned the Boss EV-5. Say what you will about Roland’s fx, but I always trusted their stuff to work. The Ring Thing went crazy on me while I had the expression pedal plugged in. I assumed it was the RT because not much can go wrong with the expression pedal I thought. So the store was kind enough to exchange my Ring Thing for a new one. The problem was gone. Then it reappeared! Then gone again, then reappeared. I had already exchanged the RT so now the Boss is getting the blame. I returned it to Guitar Center and got my scratch back, and now have decided on the Moog EP-2. GC didn’t have it so I just ordered one on the bay. Those things are only $40 by the way, vs $80 for the Boss, and the Moog EP2 is made of metal now rather than the shabby EP1. So I’ll let you all know how it goes down but as of now I withdraw my recommendation for the Boss EV5 with the Ring Thing.