The punbb authentication module (inc/auth/punbb.class.php) includes files from the punbb directory; with punbb 1.3 (currently in development), these files reset the PHP error notification level, causing warnings to appear all over the dokuwiki pages.
A patch to save the error reporting state at the beginning of this include file and restore it at the end is attached. (This patch also closes the php tag at the end of the punbb.class.php which was not previously closed.)