In phpBB/phpbb/sessions.php, we can find :

							// If the database is not yet updated, there will be an error due to the session_forum_id

							// @todo REMOVE for 3.0.2

							if ($result === false)

							{

								unset($sql_ary['session_forum_id']);

								$this->update_session($sql_ary);

							}

In addition to be very far from 3.0.2 in 3.1.x, the $result variable which originally was set by the in-line query replaced by update_session() is now meaningless and worst contains the result of the preceding query which exists in the method.

I don't think this has great implication, but $result should either be returned by update_session or this entire code block removed.