The latest screenshot compares the Xperia UI Walkman lock screen of the Android 4.3 flavored Sony Xperia Z1 and that of the KitKat powered Sony D6503 Sirius (R). On the D6503 screen is a music scrubber that you can use on any part of the music to be played. You won't find this on the Android 4.3 powered Xperia Z1 as it is native to Android 4.4. In addition, you'll notice the camera launch icon on the bottom of the D6503 screen while there is none on the Xperia Z1's screen.
Remember that option to switch to the new ART Android runtime program we showed you the other day on a Korean LG G2 updated to Android 4.4.2? The gentleman with the D6503 prototype says that this option has yet to be seen on his phone, although his prototype is running KitKat.
Screenshot of Android 4. powered Sony Xperia Z1 (L) and Android 4.4 powered Sony D6503 Sirius
Thanks, Anonymous Tipster!