Rebel XSi auto LCD sensor not working?

[TobascoJackson]

One of the quirks I rather liked about the XSi before (and after) I bought one was the tiny sensor that automatically shut off the LCD when it detected that you were looking through the eyepiece. Mine worked fine for a few weeks or so after I got my camera new, but now it doesn't work. I looked for a custom setting in the menus, but wasn't able to find anything about it. I know it's not just malfunctioning now and then because I'm in flourescent lighting or some other thing that could cause problems. It fails to work now 100% of the time.

Don't get me wrong. I love the camera, and even without that gimmick, I'm still completely happy with it. But if it's a quick fix and someone else knows what's wrong, I would like that feature back.