its not the paint that causes problem. it can happen on any paint. if the BIW(body in white) treatment and coating is not done properly the rust starts from inside and starts propagating. in a painting process utmost care should be taken to ensure that there is no positive negative potential developed between adjacent layers. seems during production of certain lots the paint shop was not working properly at fiat plant. but i appreciate the extent to which FIAT has decided to help painting the whole car and changing almost all the body parts.