I'm guessing you have the 'Activate Camera Look' control bound to a key or gamepad button. The only way to avoid the issue for now is to unbind that input. If there is no keybinding for it, zoom should work as you expect. I'm investigating if there is anything we can do, not sure yet.

Check your control settings. Do they look like this? http://i.imgur.com/B1opfiQ.png

Thanks! I logged this bug; it also looks like you're not alone in experiencing this, so we will definitely look into this for you guys. If you find another bug, please make another post just like this one. :)