After upgrading to Lotus Notes 8.5.1 Client and Template, users’ mail files appear as an Archive

After further investigation, it was determined that the existence of the "ArchiveDatabase" field, stored in the "Archive Database Profile" was the cause of the issue.  By default, the "ArchiveDatabase" field does not exist in a mail file's "Archive Database Profile", but it does exist in an Archive database.

Once this field was removed, the mail file no longer appeared as an archive.  The following LotusScript button code can be used to delete this field:

Sub Click(Source As Button)
        Dim s As New NotesSession
        Dim db As Notesdatabase
        Dim doc As NotesDocument
        Set db = s.CurrentDatabase
        Set doc = db.GetProfileDocument("archive database profile")
        If Not Doc.IsNewNote Then
                Print "Found Profile"
                Print "Set field"
                Call doc.RemoveItem("ArchiveDatabase")
                Call doc.Save( False, True )
        End If

The Notes client must be restarted to see the changes.