Currently, fetishes summoned through the Fetish Sycophant passive are replacing the oldest fetishes, and that includes those summoned by Fetish Army. Normally this wouldn't be a problem, except that many Witch Doctors now have very powerful fetishes being summoned through Fetish Army, and those bonuses do not apply to fetishes summoned through the passive (as noted in the quote!). The good news, though, is that this is a bug that we intend to fix in patch 2.1.
Our plan is to separate the fetish cap for each these skills, so that new fetishes summoned with the Fetish Sycophants passive will only replace older fetish sycophants. Fetishes summoned through Fetish Army will remain for the duration of Fetish Army (possibly forever for those of you with the Zunimassa 4 piece bonus).