I have a Sony Xperia S with the latest firmware, and the latest Waze version (both as of 23-Nov-2012). Even though "prevent screen lock" is enabled, if I change some of the options in Waze, the screen WILL lock after the phone's time-out period. If I close Waze and re-open it then all is ok, the screen does not lock. Some things cause this to happen (eg changing 2D to 3D), some things are ok (eg zooming in/out of the map). I know what to do when it happens, so I will still carry on using this excellent app, but it is annoying.