Sony is currently rolling out a new update for the Xperia Tablet S. The Android 4.1.1 (Release2) update mainly resolves an issue where the clock is unable to sync correctly. Other changes includes improvements to the preview window of the camera application and playback of Video Unlimited content. The update is around 430MB and should be available to download now.
Current and previous firmware compared
Kernels appear unchanged
Thanks @poke612!