I'd say it's real. I once saw a video of an incident that happened at USAFA, when a glider lifted off vertically and then crashed down on its wing. It was common practice for the instructor to secure the elevator with the seatbelt from the back seat (which is why this one in particular lifted off even though it was parked with one in front and another one behind, even though neither of the other ones moved), and it was also standard to have a student holding down the wing, which was later upgraded to two people at windspeeds above 15 knots, 3 people above 20, someone in the cockpit holding airbrakes open above 25, and putting the gliders in at 30 knots.
couldn't find that video though. It was around 2006...