I have an A 45G that is having random service brake application issues. You will be driving along and then you'll get a very brief flash of the park brake light so quick if you're not watching you'll miss it, then the service brake light comes on and the brakes apply without you applying any input to the brake pedal and will not release until you release the throttle pedal or you come to a complete stop
That seems like something sensor/electrical related. Cheapest initial thing to do is to check all the connections related to the park brake as well as any grounds.