Hi,
that's pretty weird. A few things can cause odd behaviour. In order of least likely to most likely.
1. noise in AC. Do you have a surge protector on TV. Many have RFI (radio frequency interference) filters,since noisy power can make TV do odd stuff. If you don't have one ,try it.
2. Stuck button on TV. Does the TV have any buttons? If so, check to make sure one isn't partially stuck.
3. software. These LCDs are basically computers and sometimes get glitches. This link
upgrade has software updates that might help. Or contact LG support on their website to see if they are aware of this issue and if this is a software issue or a hardware issue.
4. Hardware. The main pcb does everything in the TV and is where the software update would go to. It might be failing and need to be replaced.
Good luck.