I had the same failure on my 9 day old System 6 helmet this morning. Never had a similar problem on any other helmets in my 35 years of riding motorcycles. Seems to be a weak point on these helmets. Donford CT will replace the unit tomorrow morning under warranty.
Mine fell off the other day again, but I could recover it. One must just be careful not to pull on the vent, because it clips out. One must always PUSH it open or close.