I could clearly see that something was coming out from the fuel dump (jettison) valve:
I had taken this picture from my seat before the flight.
The incident took only a few seconds - the valve was only dripping a little bit when I had my camera out. But, it definitely looked like in this picture: http://upload.wikimedia.org/wikipedia/commons/thumb/c/cf/FuelDumpA340-600.JPG/797px-FuelDumpA340-600.JPG.
On a side note, have a look at an Airbus overhead panel:
The fuel jettison buttons are placed the middle of the left panel.
Now compare to this (supposed to be from a 767-300):
contrailscience.com/skitch/Overh … 103650.jpg
Given Airbus’ rather inconspicuous fuel jettison buttons, could it be the pilot hitting these buttons by accident?
What happens in the cockpit when you do that, is there a warning?