Here is what finally fixed this issue for me, and now everything works as designed (well, so far at least). It didn't make sense to me that you have to allow Windows to sleep even while in the middle of a remote session. So I didn't want to hack the register to allow that.
I went through all the tips and ended up with the dreaded DRIVER
\filesystem\srvnet being the culprit like so many others have experienced. I had to find out why this driver kept making the request to prevent sleep. Oh, and I'm a 'find the cure' kinda guy, not a 'put a band-aid on it'. The override worked for me, so I could use that as a last resort if needed.
I finally came across a post that lead me to fsmgmt.msc that clearly showed that the insomniac clearly thought there was an open file sharing session. This was even with all other homegroup pc's in standby or off, didn't matter. I could manually close the session, but it would reappear within minutes.
Turns out for me, the solution was quite simple. I guess I violated some rules when I set my homegroup (don't know if they're written anywhere). I stumbled across some info that suggested file sharing was automatically handled between homegroup pc's by the user account and passwords information. That made me wonder if the code was written expecting all homegroup pc's to expect exact same user names and passwords. I use a couple of usernames, and my password is different based on my moods. Lol! Believe it or not, as soon as I matched this info, my problem cleared up! May be a bug, but that's what it took for my insomniac pc to finally close the sharing session which was created when I shared my MC content. Now, all is fine and my insomniac is finally getting some well-deserved rest. NOTE: in my case, the insomniac was sharing to my main HTPC, which had the same username, but different password.
Maybe this info can help others. OH! I also corrected my extender setup with my XBox 360, so maybe that was the culprit. It's hard to tell because the funny thing is that the open session info never listed client info. I think my extender setup broke when I replaced my router, but I found the way to reset all that on this forum.