I was working from home late last night to work on documents for an acquisition by a client of another company when looking at the mail I saw the little star as I moved my mouse over the line which contained the word Favorites. This is at the top of the mailbox list column. Note that star and the dropdown caret only show when you mouse over it. But I was tired at 11:30pm and I thought I would see what that little star was about the next day. I could not wait to get home from work today to try it out after reading your support email, and lo and behold, it worked. So I put "all inboxes", "all Junk", "All Trash" and "All Archive" also at the top, and now everything was back to normal. Thanks for showing the fix for which I only had a hunch.
Now the issue was why this happened. I was in a hurry with so much to do last night that I must have moused over the Favorites title and somehow removed the "All inboxes" member of the favorites. So word to the wise, do not work when you are dog tired!!!
John