So bit of an odd one, ever since day one our TV (55KU6000) will occasionally become unresponsive to the TV remote except for the Channel and Volume rocker buttons (the ones that go up/down). This usually happens when flicking around freeview channels. As an aside the Freeview Ondemand App that appears onscreen when switching to 1,2 or 3 will also occasionally not pop up on screen immediately after flicking channels (this, I think ties in with the unresponsive remote.. I'm not 100% certain because I don't watch TV, the Mrs does and getting her to troubleshoot tech things isn't worth the agro)
One resolution I've figured out when the remote isn't responding is to change channels and this seems to fix the problem.
I'm guessing it's the OS being a slow or getting hung up trying to load the Ondemand App in the background?