Well, here's the rebuttal.
Remember that 100% of my music is FLAC? Name one other program that will even touch it. WMP will puke and, therefore, not find any media files so how could it mess with folder.jpg? I can't. Back when I started ripping, I did some tests and checks to make sure it wouldn't cause problems. It never did, even on a full library scan.
Store all my audio files in a single directory? Yikes! Loading my music directory with just artists takes quite a while! It's better with my new server but a good 3 seconds and years ago when I had a piece of junk MP3 (many downloaded) and nothing tagged right, I had folders like crazy and loading the directory would take for ever. Loading 18,000 file names in one directory...I don't think so.
Don't ever move files in Explorer! Obviously I'm not that stupid. Oh, gee, I've spent thousands of hours building my collection ... I think I'll move files around because I didn't do it RIGHT the first time. YES, I did it right the first time. I verified tags and I see no reason to move from my /Artist/Album system. It is without a doubt perfect in every way I can see.
WMP not touching FLAC and me being pretty sure I don't have a single other program that even plays FLAC & manages files (VLC plays only), it absolutely, positively is a MC phenomena.
Now a question: it appears that the short while MC13 was configured to its default allowed it to write images to the tags. How do I remove images from the tags? None should be in the tags. (not just a file name but an image) The reason I'm asking is ever since my experimentation with MC13, I'm now seeing the same BAD cover art on MC12 theater view client machines in theater view. So I'm afraid its adding cover art.