I am wondering if the board may have moved a little inside the case. The board inside of a 930 fits pretty tightly, and the buttons on the side line right up with them, so it might have misaligned. Either that, or the plastic insert on the case that actually pushes the button on the board might have slipped a little.
I can't think of another reason why that would be, except that some of them don't seem to click much anyways, so maybe you never noticed it before now?
A caution - it is easy to break the buttons on the side of the board, if you were inclined to try to take the back off and take a look. If you break the buttons on the board, you pretty much have a parts phone. Unfortunately, I broke the buttons on the first two Icons I took apart, and was left to part them out, recovering about half of what I paid for them. It's sort of a crummy feeling when you realize you just ruined a $300+ phone.
So, it's probably best to just leave it be, unless you're very comfortable opening it up.
If you have any questions on how to do it without ruining your board, feel free to PM.