Iveco 75e15 Air brake comes on in reverse gear??

Hi, I have a 2001 Iveco 75 e 15 which drives fine forwards and rolls freely forwards and backwards, but as soon as I engage reverse gear the hand brake applies itself. The in cab reverse bleeper used to bleep on and off, but now is a constant tone and the brake will not release until I take it out of reverse. I have been underneath and watched as reverse is engaged and there is a handbrake air hiss as reverse is engaged and the push rods engage the rear brakes???