Starting Backwards

Has anyone had a Petter AD1- or any hand cranked engine- start backwards? It happened twice today. It obviously won't do the air filter much good, but I'd be more worried about the risk of a broken wrist.

Yes, Brian it can happen,
apart from the air cleaner and your wrist, it not good for the bearings; as the oil pump (if it's a gear or rotary type) will not be suppling oil to the lubrication system.

It could be that it is not turning fast enough before you disengage the decompressor.
It could also be that the start of fuel injection is too far advanced, I think you should check the timing.