Two separate mailbox lists in same account

My dad uses iOS Mail to access his Yahoo! account email. Over the weekend, it has split into two mailbox lists. All of those in the "top" list are also in the bottom list but not all those in the bottom list are in the top list. The top list is editable (you can slide them around or show/hide them) but the bottom list you cannot edit it. Also, the "sent" folder is only in the bottom list, it's not in the top list.

1) He has only one mail account on his iPhone

2) I've tried merging the two...cannot be done

3) His trash, junk, drafts were jumbled among the top mailbox list and I was able to drag them to the top.

4) he has a duplicate inbox, trash, drafts and junk (the count is the same in both lists)

5) When you look inside of a mailbox in the bottom list and then "go back" it takes you to the duplicate mailbox in the top list.

6) I rebooted the phone...no avail

7) He only creates mailboxes in Yahoo! on his desktop...no mailboxes were created on his phone

8) He has an iPhone 5s running iOS 8.3