I"m seeing this same thing as well. My rad little halfling monk has never once caused a Topple or any other special Flurry of Blows effects from Open Hand. Very frustrating. I'm 15+ hours in and I"im worried that, as the game scales up, me not having some of the major class features not working will bode poorly for my little puching machine. I hope they get this fixed soon, I don't want to start over if I can help it.