I have the exact same problem and I have also a plugin for automatic logout mentioned in a other post which is marked resolved so I open a new one for this. I have gravatars marked in widgets but still I have users online as they have not clicked on the logout link. Also to mentioned we are using WPTouch mobile and in this specific case user have logged in via iPhone but not hit logout. I have also checked via Analytics and clearly I can see user is not logged in.
So it seems not be working with your last update!
PHP version: 5.3.18
WP version: 3.4.2
ORUW version: 2.0.1