Good question Bill, it's NOT auto adjust after all, but looks close sometimes. Further checking after your question led me to discover it's Bridge "building" the thumbnail and then the preview to match. I had the lower quality setting for thumbnails.
With high quality thumbnails checked in Bridge Preferences, I don't get to see that building process that I can see when the other types of thumbnails are selected.
Glad to help - I see this "building" process in both Bridge and Lightroom. Strangely, the first iteration of the images sometimes look better than the "built" image!