Something else is going on, I may get the start of a tiny crack over a pin, like Pat I superglue the crack, I have never had a crack travel beyond the actual pin. I am very cautious about wood removal and ring chasing around a pin, the ring usually thins to the thickness of paper and is tedious to chase over a pin. I made small scraper out of a concrete nail to carefully chase the grain around a pin, of course I call it a pin knot scraper.
Do you live in an area with wet and then extra dry conditions? Were your staves completely dry when you made a bow out of them? And mostly, is your tillering spot on with no weak or stiff spots in your limbs?
Pins don't cause me a problem, even ones on the edge of a limb, it is all about how you handle them.