Well I found two videos that have similar settings, both videos have a small amount of blur and "blocking" but they seem to consistently keep the frames intact in 360p.
http://www.youtube.com/watch?v=OXL9ezWQB7E around the 1.00 mark
http://www.youtube.com/watch?v=ADn4_qYzUqk around the 1.00 mark as well
I've also read somewhere that it might have something to do with the duration of the videos, these videos seem to be around 5min or longer and so youtube would pay more attention to the quality. But I don't really know if that's true.