There's another problem with the spell. The spell description contradicts itself as to whether the zombies remain animated "until destroyed" or whether they become lifeless again at the end of the spell duration.
My guess is that they fall lifeless with the spell duration expiration, and that the remaining animated comment is a poorly edited cut and paste from "animate Dead" spell from the SRD, but it is just a guess on my part.
Makes perfect sense to me. The spell description says that the zombie stays "alive" until destroyed. This is all during the spell duration, which once the spell duration is ended all zombies are now mere corpses.