Though I have no knowledge specific to this event, in general, "automatic" inflatable life jackets should never be worn in aircraft, and shoulder harness should always be warn over the life jacket. Automatics are great if you fall off a boat into the water, but terrible if they inflate inside a cabin, and prevent your exit, or are ripped as you exit. Also consider that an inflated life jacket would make it extra difficult to swim down to exit a sinking plane.