Index: wp-includes/default-widgets.php
===================================================================
--- wp-includes/default-widgets.php	(revision 21768)
+++ wp-includes/default-widgets.php	(working copy)
@@ -851,7 +851,7 @@
 		// Append ellipsis. Change existing [...] to […].
 		if ( '[...]' == substr( $desc, -5 ) )
 			$desc = substr( $desc, 0, -5 ) . '[…]';
-		elseif ( '[…]' != substr( $desc, -10 ) )
+		elseif ( '[&hellip;]' != substr( $desc, -10 ) && 355 < mb_strlen( $desc ) )
 			$desc .= ' [&hellip;]';
 
 		$desc = esc_html( $desc );