Changing Breakforce value stops OnJointBreak being called

I have two rigid body objects connected with a hinge joint, and I have a simple script that reduces the joint break force and torque values on that hinge slowly over time, as expected eventually the joint breaks the rigidbody falls to the floor, the problem is OnJointBreak(float val) is not being called when the hinge breaks. If I move the object violently so it breaks at the current break force value then OnJointBreak is called but not it the breakforce value is slowly reduced till it breaks.