Steps to reproduce:
Close -> Why should this… click "exact duplicate" -> Paste the URL of the "duplicated". If you click VOTE TO CLOSE right there, nothing happens.
You have to press "enter" on the URL text box so the form will "load" the question.
I don't know if this is by design. But I spent a couple of minutes clicking Vote to Close and nothing happened (even after reloading the page).
When I decided to press "enter" it worked.
Chrome 8. OS X 10.6.6.