From the story in the Toronto Star:

Burkhardt, chairman of the Montreal, Maine & Atlantic Railway, said Sunday night that the train’s sole engineer shut down four of the five locomotive units on the train, as is standard procedure, in the neighbouring community of Nantes before heading to Lac-Mégantic to sleep. Burkhardt said the next engineer was probably due to arrive at daybreak.

But someone managed to shut down the fifth locomotive unit, he said. The railroad alleges someone tampered with the controls of the fifth engine, the one maintaining brake pressure to keep the train stopped.

“If the operating locomotive is shut down, there’s nothing left to keep the brakes charged up, and the brake pressure will drop finally to the point where they can’t be held in place any longer,” Burkhardt said.

Am I missing something here? My understanding is that is NOT how "airbrakes" work. When an airbrake loses pressure, the brakes engage. Airbrakes were the first example of a "fail safe" system in every course and article I have read. Pressure in the line keeps the breaks disengaged, or open. Loss of pressure causes them to engage. I had a recent example of this when a truck driver couldn't get a trailer away from our dock after a pressure line broke. The brakes locked tight and he would have had to literally DRAG the trailer to get it out of the way. After the line was replaced, the brakes disengaged and the the trailer could move.

What am I missing here? The description above is the exact opposite of how an air brake works. If someone shut down the engine causing the pressure to fall in the lines, then EVERY locomotive and car's brakes would have locked.

Is there are new kind of air brake designed by an idiot that functions as Burkhardt describes?