No, it works, HaT is a must-have for continuous damage in your burst since an ambush crit would generate 4 cps with the right talents, if you eviscerate/kidney at 4-5 cp if it crits then 4 cp counts as 5 cp meaning you generated that extra cp from HaT, which in turn would give you 100% chance for 25 energy to possibly do another ambush.
So to answer your question
It's not bugged and you should use 3/3, as it will give you more potential damage in your burst(Shadow Dance) if combined with http://wotlk.cavernoftime.com/spell=13980 and http://wotlk.cavernoftime.com/spell=58425 and combine that with ruthlessness to get a potential extra cp to get the next 5cp sooner, as it also works as intended in my experience.
Edit: the only reason why I would put one into it is if I would run full PvE in arenas with a full PvE friend to just kill a guy in the first opener. Though I would say you would be better off keeping the 3 in HaT and removing 3 from http://wotlk.cavernoftime.com/spell=13971 to get http://wotlk.cavernoftime.com/spell=31221 if you feel lucky vs other rogues or you are human and have the stealth detection passive with good positioning.