when setting the session handler as an object using the auto register shutdown flag, explicitly calling session_write_close() should no longer be required. It shouldn't cause any issues if it is called twice, but the session driver interface has been known to sometimes act in unexpected ways and there are lots of "subtleties" which can often be difficult to debug. The mentioned flag implies PHP 5.4 minimum but I believe we require that anyway.

boot.php

@@ -1616,7 +1616,6 @@ function login($register = false, $form_id = 'main-login', $hiddens=false) {
  * @brief Used to end the current process, after saving session state.
  */
 function killme() {
-	session_write_close();
 	exit;
 }
 

index.php

@@ -190,5 +190,4 @@ call_hooks('page_end', App::$page['content']);
 
 construct_page($a);
 
-session_write_close();
 exit;