Every engine I have owned has done that at some point, specially when using a chicken stick. Does seem to happen when the engine is over-primed or running very rich.

If it does that, normally a quick jab on the throttle sorts it out.

I have come into the habit of starting the engine by grabbing the spinner and then smartly flipping the engine in the opposite direction (Clockwise)

Works like a charm and my engines never start backwards like that. Works on my .46 two strokes all the way up to my .91 four strokes.