Fullscreen TV does react on the stop button now
Many people complained about the Stop button which is ignored while watching TV in fullscreen.
This behaviour has been on purpose to safe the timeshift buffer in case you press the Stop button on remote by accident (notice the Vista MCE remote's swapped Pause and Stop buttons).
The upcoming SVN build on friday is going to show you a new dialog (which can be confirmed by either the Stop or Play button) to quickly stop fullscreen live TV.
All skinners need to update their skin to include also a dialogPlayStop.xml in order to be compatible.