User blog comment:Dopp/Technical Update: January 24, 2012/@comment-3279487-20120124205446/@comment-168424-20120126204342

This change was intentional by Wikia, but it was never fully explained. In the past (before the latest incarnation of the visual editor/RTE) the earlier version of the category module, CategorySelect worked perfectly fine in source-only editor, but that was when it lived below the edit area.