Just take a look at it: 

func (e StartElement) Copy() StartElement {
    attrs := make([]Attr, len(e.Attr))
    copy(e.Attr, attrs)
    e.Attr = attrs
    return e
}

"copy" function call arguments should be swapped. This method zeroes
"Attr" field during the copy process.

Code that illustrates the issue:
------------------------------
package main

import "encoding/xml"
import "bytes"

var test = `<x a="1" b="2" c="3"/>`

func main() {
    b := bytes.NewBufferString(test)
    parser := xml.NewParser(b)
    t, _ := parser.Token()
    se := t.(xml.StartElement)
    println("before copy")
    println(se.Name.Local)
    for _, a := range se.Attr {
        println(a.Name.Local)
    }
    se = se.Copy()
    println("after copy")
    println(se.Name.Local)
    for _, a := range se.Attr {
        println(a.Name.Local)
    }
}
------------------------------
output:
==============================
before copy
x
a
b
c
after copy
x



==============================

Issue was spotted on the latest weekly (2011-11-18)