Comment 6 for bug 1225162

I just debugged this problem. The default value for vm-summary-faces-alist has (header "Priority: urgent") and other header for vm-summary-high-priority. This can be fixed by selecting the folder-buffer in vm-vs-header. EG:
     (defun vm-vs-header (m arg)
       (save-excursion
         ;; JWM fix
         (vm-select-folder-buffer)
         (save-restriction
           (widen)
           (goto-char (vm-headers-of (vm-real-message-of m)))
           (re-search-forward arg (vm-text-of (vm-real-message-of m)) t))))