Index: wp-includes/media.php
===================================================================
--- wp-includes/media.php	(revision 26920)
+++ wp-includes/media.php	(working copy)
@@ -884,8 +884,11 @@
 			$output .= '<br style="clear: both" />';
 	}
 
+    if ( $columns > 0 && $i % $columns !== 0 )
+        $output .= "
+			<br style='clear: both' />";
+
 	$output .= "
-			<br style='clear: both;' />
 		</div>\n";
 
 	return $output;