"Clicks" get louder when I turn volume down on iPhone 5

Just wondering why, when I text, my click sounds seem to do the opposite of what my volume buttons say it should be doing. I am assuming this isn't normal but wondering what would cause it to do this.

I got the phone a week ago and am still learning some of its secrets but this one has me stumped. It only works backwards when I am texting. All other sounds seem to be controlled normally.