One of the major contributing factors to this incident is the extreme congestion on this tarmac area. There is only one entry/exit to the tarmac, which can accommodate 5 B737s. These of course use pushback procedures for departure.
However, the tarmac is shared, and there are often up to 3 Saabs occupying tarmac positions, or waiting to enter or exit while 737s are pushing back.
While not making excuses for the DJ crew, who commenced to move without sighting the engineers thumbs-up, this was the case at the time of this incident and contributed to the breakdown in communication between the flight deck, ATC, and engineers. Also Runway 25 was in use for departures so the adjacent taxiway G was also congested with aircraft waiting to depart.
The sooner Virgin gains access to some of the former Ansett gates in SYD, the better for all concerned. It will reduce the possibility of any further dangerous incidents like this, plus provide the Virgin guests and staff with a proper check-in environment not provided by the grossly overstretched facilities currently available.