I don't think the order of operations can be the cause for the LPCM shutting off the sound.
I had another experiment yesterday. I was running music off the PC and had the TV off. after an hour or so the sound went off. i left it as is for 20-30 minutes then I simply turned on the little fan...
My setup details
Sony STR-DH820 with two HDMI's coming in - xbox 360 and my PC (from a GTX 550-ti vid card)
5.1 speakers out - 3 polk in the front, two Bose in the back, and a Polk sub.
HDMI out to TV LG 55LV4400
My main problem is the receiver skips into LPCM randomly and the sound goes out...
I too have a similar problem. I have the DH720, xbox 360, my PC, and an LG 55LV4400.
My receiver craps out into LPCM intermittently. whether watching video through my PC or using the xbox. It got progressively worse as the weather warmed up. I think i diagnosed it to a heat issue and fully...