Index: wp-includes/media.php
===================================================================
--- wp-includes/media.php	(revision 15590)
+++ wp-includes/media.php	(working copy)
@@ -856,6 +856,11 @@
 				" . wptexturize($attachment->post_excerpt) . "
 				</{$captiontag}>";
 		}
+		elseif ( $captiontag && ( 'dd' == $captiontag ) ) {
+			$output .= "
+				<{$captiontag} class='gallery-caption'>
+				</{$captiontag}>";
+		}
 		$output .= "</{$itemtag}>";
 		if ( $columns > 0 && ++$i % $columns == 0 )
 			$output .= '<br style="clear: both" />';