iOS 7.1 Messages bug

I've been having a weird issue with the Messages app on my iPhone 5 ever since I upgraded to iOS 7.1. While in the app, if I cover the proximity sensor at the top of the screen, the screen turns off as if I'm talking on the phone. I've tried disabling Siri's Raise to Speak option, but no luck. Has anyone else experienced this issue or found a solution?

UPDATE: A couple reboots later, the problem is gone. Still no idea what was causing it.