[Mark-k]

The problem seems to be that wordpress adds slashes to the input in its initialization, and them comes bbpress and adds slashes once again, and since the code assumes that slashes were added only once, stange things happen.

solution that work for me: in bb-settings.php change

// Sanitise external input

$_GET = bb_global_sanitize( $_GET );

$_POST = bb_global_sanitize( $_POST );

$_COOKIE = bb_global_sanitize( $_COOKIE, false );

$_SERVER = bb_global_sanitize( $_SERVER );

to

if ( !defined( 'ABSPATH' ) ) { // no need to sanitize if wp had done it

// Sanitise external input

$_GET = bb_global_sanitize( $_GET );

$_POST = bb_global_sanitize( $_POST );

$_COOKIE = bb_global_sanitize( $_COOKIE, false );

$_SERVER = bb_global_sanitize( $_SERVER );

}