It's still completely mind boggling to me. Recently at 2C the line for the brand new Parafe gates was empty, and there were only a few people in the normal passport lane. The staff at the entrance of the lines inquired what passport I hold, I replied Dutch, and then he said: "that won't work". I Pointed at the EU flag at the entrance of the Parafe lane, and I suggested that we should try. He let me in, and.....it didn't work.
Worked like a dream when connecting at FRA a few days later, it took only a few seconds, as always...