Index: wp-admin/network.php
===================================================================
--- wp-admin/network.php	(revision 18660)
+++ wp-admin/network.php	(working copy)
@@ -523,7 +523,7 @@
 	// create network tables
 	install_network();
 	$hostname = get_clean_basedomain();
-	$subdomain_install = !allow_subdomain_install() ? false : (bool) $_POST['subdomain_install'];
+	$subdomain_install = allow_subdomain_install() ? !empty( $_POST['subdomain_install'] ) : false; 
 	if ( ! network_domain_check() ) {
 		$result = populate_network( 1, get_clean_basedomain(), sanitize_email( $_POST['email'] ), stripslashes( $_POST['sitename'] ), $base, $subdomain_install );
 		if ( is_wp_error( $result ) ) {