Not sure what causes it...temperature changes would be my guess as the pin is made from a different material than the coverstock.
It shouldn't hurt anything. If it bothers you, have your driller drill the pin out and fill it with plug. We did that on one of my dad's. The finger was very close to the pin, actually drill part of the pin out. The pin started to slip, so we just drilled the rest of it out. I know of other people where the layout caused the pin the be in the middle of the finger hole, so the pin got drilled away, doesn't affect ball reaction. It's just a pain if you ever redrill the ball as you don't know exactly where the pin (top of the core) is.
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It IS next year!