first:

drag one element(.portlet)

second:

execute code: $(".portlet:first").clone(true);

now:bug appeared.it throw an "Stack overflow" exception.

source code:

if ( deep && copy && ( jQuery.isPlainObject(copy) || jQuery.isArray(copy) ) ) {

var clone = src && ( jQuery.isPlainObject(src) || jQuery.isArray(src) ) ? src

: jQuery.isArray(copy) ? [] : {};

Never move original objects, clone them

target[ name ] = jQuery.extend( deep, clone, copy );bug appeared here!

// Don't bring in undefined values

}