Correct me if I'm wrong, but those clearly look like the stock diverter valves that are mounted to your charge pipe. When you're on the throttle and building boost and then let off (you brake or shift, etc) the throttle body then closes. The turbos are still spinning though and building pressure in the intake piping after the turbos. These valves essentially divert the build-up of pressure in front of the throttle plate back into the pre-turbo piping of your intake, recycling the air, so that it doesn't force back-pressure on the spinning turbines (which is no good for a bunch of reasons).
If you're on a stock tune and blowing these things off, I'd say it'd be one of two things. Either the connection point (grey ring lock) of the valves has some broken plastic or is worn, or the valves are getting stuck/not opening when they should and the pressure that should pass through them is just blowing them off the pipe.