Ok, I'll reply to my own post since I found something. There were two identical images (you know how many duplicates show up when you transfer over from iPhoto). Most I tediously got rid of, but a few linger.
Trying to edit Photo A failed, taking forever. So, I tried Photo B and got the same dismal results.
After hours of trying all sorts of internet suggestions, I finally got mad and simply deleted A, never wanting to see it again. And, surprise, B somehow got liberated and editing it was almost instant.
Both photos had the same statistics, just one somehow was diseased in some way. I later found another similar pair of photos, one evidently good and one evil.
Something I did? NO. Just one of the bugs people are not happy about. Hope it gets fixed.
