Still experiencing issues
I was searching for a fix on my Samsung model pn50b850 and came across this thread. The TV is approx 2 years old, and has done what is described above from roughly the time I bought it. It will at random change volume or source input. If ignored, it will eventually "lock up" where it changes source and then the little red light in the bottom right corner that lights when receiving input will start flashing continuously, and the TV does not accept input from either the remote or the buttons on the TV itself when this happens. The only fix has been to unplug TV and replug in. It then operates normally.
Typically, the TV will experience this issue about once every day. Enough to be annoying but not enough to justify a TV repair bill. I have moved locations with the TV, as well as had this issue while
using basic cable and Direct TV, so I suspect it is a TV issue, rather
than an issue involving the TV receiving signals from external sources as theorized above.
I will inquire through Samsung support, but if anyone has stumbled upon a cause or quick fix to this issue I would greatly appreciate reading about it.