I don't have the iPhone version, but in the board game that's how we play. Once somebody takes a tile from underneath the red wooden coin on the final stack, the game ends once all players have a truck. Doesn't seem true. It's rare, but all 5p can take a full truck to use up all 15 remaining tiles in the game.
So it should only end after the stack has 14 tiles left and all players have taken a truck. If there are 15 tiles left and all players take a truck, the trucks should go back into the middle for one more round.