--- User.php    (revision 42040)
+++ User.php    (working copy)
@@ -247,6 +247,7 @@
                                break;
                        case 'session':
                                $this->loadFromSession();
+                               wfRunHooks( 'UserLoadAfterLoadFromSession', array( $this, &$result ) );
                                break;
                        default:
                                throw new MWException( "Unrecognised value for User->mFrom: \"{$this->mFrom}\"" );