Mail: AppleScript Mavericks: Error cannot recognize newly created Mailbox

Question

Hi!
I had a simple apple script to sort my mails into folders. After an update (don't know which exactly) my apple script fails to create local mailboxes in mailboxes.
If the mailbox "Archiv/2014" is created, in the next step the script failes to recognize the new created mailbox.
Here the sorting part of the script:
  set box to mailbox "Archiv"
          set zahl to every message in box
          repeat with theMessage in zahl
                         if (get sender of theMessage) is "xy" or (get sender of theMessage) is "xz" then
                                        move theMessage to mailbox "ABC"
                         else
                                        set datum to (date received of theMessage)
                                        set jahr to (year of datum)
                                        set monat to (month of datum)
                                   if not (exists mailbox ("Archiv/" & jahr)) then
            make mailbox with properties {name:"Archiv/" & jahr}
                                   end if
                                   if not (exists mailbox ("Archiv/" & jahr & "/" & monat)) then
                                                  make mailbox with properties {name:"Archiv/" & jahr & "/" & monat}
                                   end if
                                   move theMessage to mailbox ("Archiv/" & jahr & "/" & monat)
                         end if
          end repeat
This throws:
Ergebnis:
error "„Mail“ hat einen Fehler erhalten: Fehler in der AppleEvent-Routine." number -10000
In another script it is tested:
Script and answers:
tell application "Mail"
  exists mailbox "Archiv/2014"
  --> false
  make new mailbox with properties {name:"Archiv/2014"}
  --> missing value
  exists mailbox "Archiv/2014"
  --> false
end tell
Does anybody see my mistake?
Thanks in advance!

Answer 1

That's really weird!
Both scripts below create a new mailbox, but only the second script returns true. The two mailbox names differ by only one character.
Script 1
tell application "Mail"
    exists mailbox "Archiv" --> false
    if not (exists mailbox "Archiv") then
        make new mailbox with properties {name:"Archiv"} --> missing value
    end if
    exists mailbox "Archiv" --> false
end tell
Script 2
tell application "Mail"
    exists mailbox "Archivs" --> false
    if not (exists mailbox "Archivs") then
        make new mailbox with properties {name:"Archivs"} --> mailbox "Archivs"
    end if
    exists mailbox "Archivs" --> true
end tell