Heading for Nanomail sent from a thread?

When I click "Nanomail" button under a message in a thread, it gives me an "empty" mail base. Would be handy if the default heading would be the subject of that thread I'm responding to. Would also show the recipient immediately why somebody has set that nanomail. Of course I can copy that by hand, but that means I have to remember to do that preferably before i click the button.