The A-5 with the cross bolt has a trigger spring with 3 fingers on it. The middle one puts tension on the safety ball that makes the click when you slide it back and forth. NOT often but sometimes this finger will break reliving the tension on the safety ball and allowing the safety just to slide back and forth .
SOLUTION--replace the trigger spring !! MAKE SURE that the spring you get has THREE (3) fingers. The earlier springs only have 2 and will NOT solve your problem !!