This news story shows video of fuel being expelled from a wingtip of a 767, while at the gate. The engines were apparently running during this event. After the cockpit crew learned of what was going on, the engines were shut down and fire equipment was brought in.
Since this happened on the ground, is this an incident that must be reported to the FAA? The article says that the airline hasn't given any details of the incident.
Perhaps this belongs in another question, but what could have happened here?