The Pony was a much lighter machine than the Horse. So naturally it can have more tendency for the tines to propel it forward unless your garden is already well broken. It also had a narrower tilling width. That's why I said it was good for maintaining a garden that was growing because it fit well between growing plants, could keep the garden tilled up, and was easier to manuver in tight spots.
The Horse excelled at getting the garden ready for planting in my experience, but wasn't as easy to handle when it came to keeping the garden weeded once the garden was up and growing.
I think the OP's tiller must have been stored in someone's garage and somehow the handle bars were run into by a car breaking or bending the now missing parts. Whoever had it either didn't get around to replacing them or the parts were no longer available by the time this must have happened.
Most likely, it's fabricate or find a donor machine.
