Index: src/core.js
===================================================================
--- src/core.js	(revision 3505)
+++ src/core.js	(working copy)
@@ -748,7 +748,7 @@
 				// Otherwise, we need to flip out more values
 				} else {
 					elem = jQuery( elem.cloneNode(true) )
-						.find(":radio").removeAttr("checked").end()
+						.find(":radio").removeAttr("checked").removeAttr("defaultChecked").end()
 						.css({
 							visibility: "hidden",
 							position: "absolute",