Share your experience!
http://forum.xda-developers.com/z3-compact/help/alarm-muted-using-keys-behaviour-test-t3176957
"Hi I was wondering if I was alone on this but ever since the new update, my alarm would not sound (but screen turns on) if the alarm is using either the Snooze or Dismiss 'Side keys behaviour'. The alarm does sound when the side keys behaviour is set to none though! I've tried both using mp3 files and the default ringtones."
There's some more information from other users on the link above!
Try settings-apps-all,scroll down to clock,tap on it,force stop and clear data.Try again with the alarm.
That didn't work out for me sorry.