Not sure for pedestrians but by logic this applies to them as well. Logically a flashing don't walk signal to someone who hasn't started walking over the crossing means Stop. What else could it mean?? Run over the road or cross as fast as possible. Definitely not as that would increase accident probability.
It's not that unreasonable to have a different law for cars than for pedestrians.
Ask yourself with what object do fast late crossing pedestrians have the most problems with? ( hint: it's heavy )
(Disclaimer: This is based on Raleigh, NC's traffic lights. I don't know what level this is standardized at.)
http://peds.org/resources/pedestrian_right_of_way/
Start reading at: Pedestrian control signals
Also:
http://www.mto.gov.on.ca/english/dandv/driver/handbook/secti...
http://www.durham.ca/print.asp?nr=/departments/works/roads/t...