I run into the same thing at some military bases. If they happen to be running 100% ID checks, then they ask me for an ID. Two weeks ago, I showed my passport card which would at least prove US citizenship. They didn't know what to make of it, so they asked for a drivers license (I wasn't the driver of the car). Some bases scan and capture the ID bar code which would at least keep a record of who came on base. That I understand. Most just look at the ID and hand it back to me. Proved nothing.