That's interesting. I'm an electrical engineer by training and I'm surprised that when they replaced the 'main' board and the display the first time that didn't manage to replace all of the active components in the phone. Since passive components are rarely affected (like this) by heat (they change value slightly but that is part of the spec) getting a 'refurb' back with new active components was the most probable fix.

Too bad we don't have the HTC diagnostics on this problem as well. While I feel for you and your poor customer service, no doubt somewhere buried in the bowels of the company there is some guy or gal who has to figure out the root cause and get them to change the phone.