Fuel primer bulb

Today I went to put our boat in for the season and I had replaced the fuel line from the tank to the motor with a new primer bulb. The bulb wasn’t getting hard and it seemed like it wasn’t doing anything. I checked the arrow to make sure it was in the correct direction and it was. I decided I’d flip flop the line so that it would be running “backwards”. That seemed to work and it started and was running just fine. Any idea why this would happen or am I missing something here? Seems strange that it would only work with it setup backwards.

That's a new one!!!
Maybe when they assembled. the installed the valve in the wrong end?