They can't strictly enforce the "put a foot down" rule because a fair number of folks can do a track-stand.

Also, there is evidently some room for interpretation of this rule. I, too, received a ticket for failure to stop at a stop sign (right-hand turn in bike lane) in Ca. The officer said he saw me pedaling through the turn (well yeah, there was a good headwind that day). I asked him if I had to put my foot down and he said "no", I just had to stop pedaling and come to a "near" stop. I've followed this rule and been observed by cops at this same intersection with no repeated citations.