I also experienced the jump bug. It looks like the player is jumping a very tiny amount when I press Z, but only high enough to get me into one out of the three fruits.
Is it possible you're putting gameplay logic in Update() instead of FixedUpdate()? You have to detect keypresses in Update(), but after that it's better to update actual game logic in FixedUpdate; that way it'll run the same on different machines, regardless of framerate.