When I was testing a blueprint that had rail signals at the very ends of the blueprinted tracks, the track extensions added automatically by the tester included rail signals that were in the very next tile over from the existing ones, i.e. inside the 'too close to existing rail signal' limit normally imposed by the game. This caused both signals to become nonfunctional. The rail extension code should be updated to ensure the signals it places are always at least 2 tiles away from any existing ones. (Simplest solution: just move the signals in the extension to be one tile away from the end of the generated track.)
