From the GNOME
bugzilla: "The "SEQUENCE" value in the GData of the IMAP code
(camel-imap-folder.c) is converted from a string using strtol. This allows
for negative values. The imap_rescan uses this value as an int. It checks
for !seq and seq>summary.length. It doesn't check for seq <
0. Although seq is used as the index of an array."