Roger, I have seen powder coating with the similar problem but didnt ask the experts if it is a powder problem OR a preparation problem.....I have also seen paint do similar stuff. Powder coating is essentially melted on....it theoretically sticks to the surface really well and flexes with the surface. Mine is really hard to chip but it can be penetrated. Where my 40" Goodyears turn and hit the frame, they have worn the powder off....but there is no "edge" for moisture to get under nor can I lift a chip off with my fingernail. In fact, it is a bit difficult to scrape the paint off with a knife....
We need an expert who really powdercoats to answer....not me who simply visits a powdercoat shop and writes a check to them.