All i can tell you is they were basically as light as could be set up (never had a prob on my mtb they came off of, either) and i yanked up on the pedal upstroke and came out, then ended up getting taken for a ride on the other leg til i got my balance back/slowed down. i have since readjusted the cleats (that foot was basically out of float in the heel-rotating-clockwise direction when i felt like my foot was "neutral", which i didn't notice) so maybe it was more of a twist out than pull straight out situation.

i am far from in awesome shape and it was even on the leg i had knee surgery on in June (still weaker than the other leg), so go figure.