I have set up a mechanical piston with linear chassis and harvesters. I have attached a couple photos. When I hook it up to a gearshift and give that a redstone signal, a bunch of clicking noises happened, the whole structure flickered in and out of existence, and then the mechanical piston broke. I looked thoroughly for something it could be caught on, and didn't see anything. So I disconnected the gearshift and used a hand crank. Works perfectly. So I tried connecting directly to a crank source with no gearshift, and something breaks every time - usually a shaft breaks, but sometimes the piston. Still works fine with a hand crank.

I think this must be a bug.

Actually, please disregard. One of the shafts was superglued to the structure, and with your new versions you can't see what has superglue on it unless you're holding the glue in your primary hand. Took me a while to find it (I was hand-cranking the piston and happened to spy the shaft glued to the back of the chassis).