Comment 2 for bug 1097442

Julian Bradfield reports:

After another two hours with edebug, the real problem turns out to be
very simple (but a pig to find):

*** vm-summary.el 2012/06/13 17:49:27 1.2
--- vm-summary.el 2013/01/09 10:55:24 1.3
***************
*** 1716,1722 ****
    (or (vm-label-string-of m)
        (vm-set-label-string-of
         m
! (mapconcat 'identity (sort (vm-labels-of m) 'string-lessp) ","))
        (vm-label-string-of m)))

  (defun vm-make-folder-summary ()
--- 1716,1722 ----
    (or (vm-label-string-of m)
        (vm-set-label-string-of
         m
! (mapconcat 'identity (sort (copy-sequence (vm-labels-of m)) 'string-lessp) ","))
        (vm-label-string-of m)))

  (defun vm-make-folder-summary ()

Presumably Uday's already noticed this at some point, since trunk does
have the protective copy-sequence.