There's a good article about this
here on AVWeb.
The NTSB report of a Cirrus SR20 that crashed killing an instructor and his student while practicing this manoeuver can be read
here. It determined the probable cause to be:
"
The student pilot's failure to maintain an adequate airspeed while maneuvering, and, the flight instructor's inadequate supervision of the flight. A factor in the accident was the strong tailwind encountered as the airplane turned from an upwind to a downwind during the teardrop maneuver."