Donny's not the only one that had this embarassing shutdown. In certain situations, with pumpin' bass, loud volumes ( like a typical wedding )mine shut down more thana few times .... same as the few times they were placed too near a corner, on the floor, on their side. ( A Mackie suggestion )
Outdoors, on poles in direct sunlight - same deal ... but not as often.
The heat sinks are inadequate for the volume levels that the 450s generate in less than optimal conditions.

I don;t care what the specs say, or what you read somewhere .... in practical application, in a real demanding musical show, I can site more than a few shutdowns that are specific to the Mackies. The sound was incredible, but the letdowns were too numerous for me to trust them again.