Duplicate UID warning in dsync backups

[Doug]

Hi,

Running dovecot version  2.3.18 with mdbox storage. I run daily backups 
using dsync on the same server into maildir format. Several times per 
week I will get an error like the one below that prevents backups from 
completing. The error is always on my user, never any of my other couple 
dozen users.

dsync(doug): Warning: Deleting mailbox 'INBOX': UID=133060 already exists locally for a different mail: GUIDs don't match (1657786027.M158587P19048.maildev.domain.com vs 581a08178e8ecf62f04700002bad4ea1)
dsync(doug): Error: Couldn't delete mailbox INBOX: INBOX can't be deleted.

Subsequent backups typically have a slightly different error.

dsync(doug): Warning: Deleting mailbox 'INBOX': UID=132994 GUID=407c871b0ec1c562b51000002bad4ea1 is missing locally
dsync(doug): Error: Couldn't delete mailbox INBOX: INBOX can't be deleted.

Notice the UID and GUID are different from the first error. At this 
point I will identify 407c871b0ec1c562b51000002bad4ea1 in the source 
mailbox, and move it to another folder. More often than not that clears 
things up.

The backup command I am using is
    dsync -u doug all backup maildir:/home/doug/.mailbkup/mailboxes

My questions are:

Is the "locally" referring to the source or the target of the backup?

What might be causing this problem?

What the heck is this guid: 1657786027.M158587P19048.maildev.domain.com"

      Note:
      The server is actually named mail.domain.com, not maildev.domain.com
      All file names in the backup maildir have mail.domain.com in them
      No files exist in the target maildir directory that begin with 
1657786027*
      My original migration from mbox format to mdbox was tested and run 
on a server named maildev.domain.com.  Is that why I am seeing a 
reference to maildev here? Is that name cached somewhere? Can it be 
corrected? Does it matter?

Are there any options I should add to the dsync command to fix this 
problem?

-- Doug
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