Alan,

I think you hypothosis is correct.

"I am starting to suspect that the LED is supposed to mean that PME/Wakeup functionality is either enabled or disabled -- but that there is some other error that is causing it to work inconsistently."

Seeing that the intel tech tod me it was a  intel Managment Engine indicator, and seeing the ME handles all WOL requests, etc..   it makes sence

Woudl be nice if we coudl get a offical answer though.