Index: wp-includes/http.php
===================================================================
--- wp-includes/http.php	(revision 8646)
+++ wp-includes/http.php	(working copy)
@@ -214,7 +214,7 @@
 			$transports = WP_Http::_getTransport();
 		} else {
 			if ( is_array( $r['body'] ) || is_object( $r['body'] ) ) {
-				$r['body'] = http_build_query($r['body']);
+				$r['body'] = http_build_query($r['body'], null, '&');
 				$r['headers']['Content-Type'] = 'application/x-www-form-urlencoded; charset=' . get_option('blog_charset');
 				$r['headers']['Content-Length'] = strlen($r['body']);
 			}