Bug specific to iPhone 5S

Hi all. I've noticed a very irritating bug on my iPhone 5S and wondered if anyone else is having the same problem? When I'm playing any music or podcast or whatever and I press the volume buttons (either on the earphones or on the device itself), it wakes up the screen. This is even more annoying for us VoiceOver users. On my old iPhone 4S and on my iPod 5th Gen, both also running iOS7, I had the more widely reported bug of VoiceOver saying "screen locked" a few seconds after pressing a volume button, but as I say, on the 5S it's waking up the screen completely, which is even more irritating. It's only when earphones are plugged in. Anyone else noticed this? Thanks and happy new year. Dave