1. I have NEVER seen a jack system that requires you to push the BRAKE pedal to operate the jacks. Emergency Brake pedal,YES. I have worked on all brands of Jacks and NONE have you push the Brake Pedal. IF yours is wired this way, you either had it installed wrong or you have some type of way OFF aftermarket jack system.
2. The Brake controller is designed to be on the COLD side of the Brake Pedal switch. So it only activates when you use the Brakes.
3. It appears you may have Powergear Jacks as they are designed to retract if the key is ON and it does NOT see the emergency brake signal. So, at this point you need to verify the Mechanic did not tap into the emergency brake system wiring instead of the Brake system wiring.
4. Do you have Roadmaster or Freightliner chassis? Please let us know. I ALWAYS use the REAR Brake lights as my feed for a brake controller. I never attempt to tap into the Dash or air valve switch for the control signal. Just to prevent problems like this. Doug