Try taking the empeg out of turbo mode. When it gets hot, it goes into an over-run mode to keep oil going through the gears while it cools down. This stops machinery cracking under heat stress.

but seriously

can you put a suitable diode in line with the other head unit's ignition line? It might stop any discharge flowing back to the empeg. Maybe there is a capacitor in your head unit on that input line, which is discharging and keeping the empeg alive?