Is the volume supposed to change with the screen off? I was thinking it only did that behind the lock screen (screen on), not when the device is asleep.
It seems that this is a related problem. Ideally (i.e. for my previous WP7 phones), the camera should wake the phone up and you should be able to change the volume with the screen off. Here are scenarios I have experienced with the Lumia 900 (also please note I'm not a moron and have the settings in "photos+camera" set correctly and am not blocking the proximity sensor):
1. The volume buttons do nothing with the screen off. The camera does not wake the phone. Worst case-scenario
2. The camera does not wake the phone the first time I try it but it does immediately after. I.e. I press and hold for 5 seconds, nothing happens. I release, and within 1-2 seconds perform another press and hold. This wakes into the camera app. This has been reproducible a number of times. The volume buttons also change the volume with the screen off.
3. Everything works as it should. Volume buttons work with the screen off, and the camera button wakes to camera on the first attempt.
I experience all of these at various times. There's nothing I'm doing to get the behavior to change-- no restarts, no setting changes, nothing. It seems completely random. The fact that the volume buttons also don't reliably work leads me to believe that there is some sort of bug WRT to all hardware buttons functioning with the screen off. Luckily that bug hasn't affected the power button (yet!). :shocked:
EDIT: BTW I have installed the update. It didn't change anything I'm experiencing.