Front Parking Sensors
 

I recently bought a 2015 Mazda 3 2.2 Sport Nav but the Front Parking Sensors are inconsistent in their operation. When moving forwards into a car parking space they fail to operate a majority of the time - I say a majority of the time as they have operated automatically on a few occasions. When I reverse they come on as expected (the front sensors). I have been told this is how they are meant to be when moving forward i.e. you have to manually turn them on when going forward but come on automatically when reversing.
Can anyone verify this please?