it's called maintenance.the return plunger in the pro-design gets dried out or sticky and wont close properly . seen it twice on last trip two different sleds.they need a little oil once in a while. sorry for your bad luck.
Wow maintenance on a tether??? Glad I don't have one of those. Just one more thing to have to look over and take care of before a trip. Then having to worry about if its going to work or not when its cold and ice everywhere. Think I will just stay away from Pro Designs.