2001 Jeep Cherokee Tail light problem

My 2001 Grand Cherokee has a problem with the right rear tail light and brake light unit.

When circuit tested the circuits are clear and active. When the brake is applied the brake light works.

When he headlights are on the tail lights work.

When the headlights are on and the tail lights are on, if the brake is applied, all of the lights in the right tail light / brake light assembly go out. Only the left tail light assembly works when both tail light and brake light are on at the same time.

Why does applying the brakes turn out all of the right rear lights?

My mechanic says I am not the only client he has with this problem and he has no idea why we lose our lights. I received a $202 ticket because my inspection expired because no one can figure out the light problem.

Your answer could get my vehicle past inspection and save me the fine.

Thanks,
Sue Upshaw