[megalodon]

Very interested if that resolves it for you. Any other info you could share would also be helpful. I have always suspected that another device in my entertainment system had an overlap with the power on code.

Well it still seems to be working fine with no random restarts and it hasn't crashed once. I have a Netgear GS108Tv2 switch connected to my Billion 7800n router and my Intel NUC i5 is connected to my Anthem MRX700 Receiver. The only other thing I use is my Xbox One, but I power that on with the controller button so no codes affecting it there. I only power on the Anthem and use the volume up and down buttons on the remote, but most of the time I power on with the receiver power button and select the source on that as well.
I don't think for one minute that another IR code was turning on the NUC as it would randomly come on when I was out of the room.
I was dubious about going to OpenELEC 4.1.6 beta but I suppose in some ways all the versions I have used were beta in a way. I think that something across the Network was turning it on, how and why I don't know as I have always had WOL turned off. I don't use S3 sleep as my NUC is in a Tranquil PC Abel H2 passive case and it boots in 10 seconds so its just not worth it by the time I turn on the Receiver and TV its up. I have noticed that I still need to turn the Receiver on first before the NUC as it won't get a HDMI signal if not. When I first had the NUC I used to forget and would have to turn the Receiver off and back on but now I always turn on the Receiver, TV then NUC and about 6 seconds later Im at the Movie menu.