Steve,

Here a few recommendations:

I had that happen a few times (scarey) and cured the problem after a few "adjustments":

1. Removed grease/oil from the pedal-rod that goes the the floor/felt "seal"
2. Replaced the floor/felt seal (no grease/oil in/on that seal)
3. "Sharpened"/gently-filed the edges of the piece of metal that "catches" against the pedal-rod

I do not know which worked, but mine only releases now when I pull the release lever.

Maybe other people have remedies for this disconcerting/dangerous behavior?