This doesn't seem too common, at least here on the forum. If I'm reading it right, its only the #3 piston? That should rule out oil viscosity an issue. Unless there was a circulation problem in that cylinder. Or like others have mentioned, the too rich mixture programming hit that port extra hard vs. #1 and 2? Or maybe that piston was installed on a Friday afternoon... if it was a rich mixture washing the walls, Honda should be seeing a lot of this in their 1.5 turbo.