My OS 75 AX starts up backwards a lot of times after it has warmed up (after the first flight). But, part of that is my fault because this engine starts so easily, that I just flip the prop one time and it will start. Sometimes, backwards, but, as Ken said, I just pop the throttle open and closed real quick and it usually just makes a little popping noise and then runs forwards. Doesn't seem to be a big deal.

My OS 1.20 AX, though, I actually tap the prop hard in the reverse direction with the chicken stick and it will immediately start up running forward.