It says in the log that it binds him, but it doesn't actually do so. Moving forward with advancing strategies and tactics, this working properly would help tremendously. It's the only form of control you can ever have against AV and in the effort of a "nonzerg" kill, this fix is imperative. I personally don't have log caps showing it landing but doing nothing, hopefully someone has that somewhere.
Edit 1: I'm told it happens with other mobs that are immune to bind as well, for example White Coney, which I would imagine he is supposed to be immune to shadowbind, but AV is not, which more likely points at the way shadowbinds debuff is being handled. Hope this gets looked into, tyvm