[Andreas]

You are right that forum.php does use fetch_foruminfo(), but array $forum in the handler for do=update consists only of certain keys of this array (defined by the forum constructed in the handler for do=add/edit).

And that's the point: If you use the array returned by fetch_foruminfo() directly it will contain keys that do not exist as columns in table forum, which causes problems in fetch_query_sql() as it will just use all keys in the given array to construct the query.