In a case of the city taking action without realizing all the results of said action. As the graphic by the RPD explains, you can park there and once there you're legal. If however a cop sees you parking or leaving your parking spot you could get a ticket.
This is pretty much the same explanation I've gotten when asking about cars parking on their front lawns on properties with no front driveways. To get to the front lawn they had to illegally drive across the sidewalk, once there it's a legal spot. It's only during the act of driving across the sidewalk that the driver can get ticketed.