Index: CKEditor/trunk/_source/plugins/liststyle/dialogs/liststyle.js
===================================================================
--- CKEditor/trunk/_source/plugins/liststyle/dialogs/liststyle.js	(revision 6905)
+++ CKEditor/trunk/_source/plugins/liststyle/dialogs/liststyle.js	(revision 6908)
@@ -143,5 +143,6 @@
 										commit : function( element )
 										{
-											element.setAttribute( 'start', this.getValue() );
+											var val = parseInt( this.getValue(), 10 );
+											element.setAttribute( 'start',  isNaN( val ) ? 1 : val  );
 										}
 									},