It's bugged. It's always auto-casted.
I was downright shocked that all the unleash effect did was add an extra 20% to the FB snare.
Funny, I've never had Bash getting auto-casted issues. I just turned it off and macro'ed it to my Feral Spirit button, and they bash when I want to. Then again, long time I used my small shammy for PvP, so I'm not sure if it always auto-casts on players.
I'm not sure what I was expecting for FB Unleash Elements, but yeah, seeing that it is only an extra amount of snare doesnt sound very appealing. And if it happens to be dispellable magic then it will be even less useful if a healer is around.