I have the same problem unfortunately. On mine, the volume goes all the way down, the menu pops up randomly and the remote won't work so I can't control the TV.
I took the TV to the "designated" repair shop twice. The first time they said they did a software update, brought it home and it still had the same problem. The second time I took it in they said the same thing, did a software update, but yet again it still messed up. Then I bought a Philips surround sound system and it still messes up the volume.
Save yourself the cash on the surround sound because that doesn't fix it, it will still screw up. I guess we are out of luck unless someone out there knows how to fix it. I agree it's so frustrating to randomly mess up in the middle of watching TV. Sorry I'm not more help other than advice to not buy the surround sound.