I have found this to be true, too, seaotter, and I think you are correct: the heat of the atty itself will over time loosen the paint. Solvents too, including hot water. The color is painted on, not baked on as an enamel, so eventually it will come off, and alcohol will hasten this. I have found this to be particularly true with wide-band 510 attys. the no-band attys seem to be holding their paint better.
related to this were the reports that certain cleaning solutions are better than others for removing baked-on gunk on the coil and mesh. The "evidence" of this was little dark flecks in the cleaning solution. In general, such dark flecks are actually paint.