If one has permission to access the Editing and Management tabs of the KB, when you click on a tab, you get:

[phpBB Debug] PHP Warning: in file /var/www/www.phpbb.com/website-current/old/support/docs/kb/submit.php on line 36: Use of undefined constant KB_READ_ONLY - assumed 'KB_READ_ONLY' (this will throw an Error in a future version of PHP) 

This appears at the top of the page (see attached screenshot) but does not affect function.