Asking anarcho-communists "you're leftists so you support [party self-labeling as 'left'] right?" is so history-less.
Yes, in conflict anarchists tend to cooperate with any less imminent authoritarian threat,
but does not mean we support parliamentary shenanigans.
We choose whom we cooperate with, when and why on individual basis.
Even cooperate with authoritarian "communists" (albeit an oxymoron) sometimes because some see a greater strategic threat elsewhere, but know as they cooperate with Trotskyites it means expecting a dagger in the back, as with Stalinists means ice-pick in your neck and we joke about it until those that fight FOR power instead of against sense it graspable.
That's when anarchists know treachery becomes party dogma, or should've in the past, when "allies" came at us red not of commune but of us slaughtered at the front with stabs in the backs.
@Anarkat Well, heh, if you break it to the argument properly, I find there are two arguments that tend to be convincing:
Words that just do not work together in any linguistically meaningful sense, but there are some (extremely few) that do put them together to describe themselves and therefore they do exist as words (while I don't have the right to say they can't, just to say that I reject them as legitimate theories and as anyone I'd have anything to do with).