Melting Pistons

There are times when damage to a cylinder is not spectacular or even very obvious. Look closely at the left side of this piston crown and you can pick out the melting around the edge that was occurring. Even more difficult is determining the cause. Was it caused by un-metered fuel in the cylinder from an injector concern or excess fuel diluted oil from the crankcase breather system coming through the intake? Over loading and over heating or the use of a non-factory engine calibration?