Seriously. With more recent firmware, I see this on two different Nuvi's as well as my Montana. Try doing an address search on your GPS for anything you like - streets, cities, POI's. The word Mill is always capitalized. For example:
MILL Haven Rd
MILL City OR
Paper MILL Playhouse
If you have a moment, try this and if you get the same thing post what model GPS you're using. Basecamp doesn't do this, so I think it's a recent global change in Garmin firmware. Very strange.