Question: I have a few buttons in my app whose alpha is currently set to zero. These buttons are completely non-responsive, but as soon as I increase their alpha, they begin to respond. Is this expected behavior?

Answer: 
As per [Apple's documentation](http://developer.apple.com/library/ios/documentation/uikit/reference/uiview_class/uiview/uiview.html#//apple_ref/occ/instm/UIView/hitTest:withEvent:) for `UIView`'s `hitTest:withEvent:` method:

> 
> This method ignores view objects that are hidden, that have disabled
>  user interactions, or have an alpha level less than 0.01.
> 
> 
> 

So any `UIView` that has alpha lower than 0.01 will be ignored by the touch events processing system, i.e. will **not** receive touch.
I'm a little late to the game but you could always set the UIButton background color to clearcolor. This would keep them active. In my case, I am pulsating a button to give it a glowing effect but to do this, I must set it's background to clear, then add a UIIMageView as a subview and add the effect to the image, NOT the button. 

Hope this helps anyone else with this problem.