That's right these shorts have a vent to let the air out so your shorts don't blowup and turn into air brakes. Actually the vent is meant to keep you cool but it's unintended benefit suits us bent riders. Next best thing to squeezing into lycra cycling shorts to avoid having your pants blowup.
I just bought a pair of the original Endura Hummvee shorts. Back in June I bought the Endura Hummvee Lite Shorts and I'm very happy with them but the summer mornings are unseasonably cool so I bought the heavy duty Endura Hummvee. Like the Lite Endura they have velcro leg hems and all the other good stuff, but in addition they have an air vent. It keeps your legs cool and lets the air out of your shorts so they don't blow up like a balloon. Personally tested up to 44 mph with minimal ballooning. Nice threads!