Fix bbPress' bbp_is_site_public() function.

bbp-site-public-hotfix.php

<?php
/*
Plugin Name: bbPress - Fix Site Public function
Description: Hotfix for bbPress' bbp_is_site_public() function.
Version: 0.1
Author: r-a-y
Author URI: http://profiles.wordpress.org/r-a-y
*/

/**
 * Fix bbPress' bbp_is_site_public() function.
 *
 * This notably fixes BP activity entries from being posted if the site is not public.
 */
function ray_bbp_fix_site_public_function( $retval, $site_id ) {
	// $retval is numeric, but it needs to be cast as a boolean for
	// bbp_is_site_public() to work as intended.
	if ( $retval > 0 ) {
		$retval = true;
	} else {
		$retval = false;
	}

	return $retval;
}
add_filter( 'bbp_is_site_public', 'ray_bbp_fix_site_public_function', 10, 2 );