external displays and projectors

I've been having problems getting my MacbookAir (Mid 2012) running OSX 10.8.2 to use external displays and video projectors via VGA and DVI adapters.

The problem is that if I am connected to my external monitor and disconnect the magsafe power adapter, the displays (both the external monitor and the macbook builtin display) instantly go black/shut off. If I close the macbook lid and open it, the displays come back momentarily but then switch off again.

If I connect a video projector via VGA while running on battery power only the displays come on momentarily and then switch off / go black/blank. Opening and closing the lid causes the displays to come on momentarily but they quickly go black/shut off again.

I found a work around for this as follows:

- I had my displays set such that the external display was to be the "main" display (the display with the menu bar at the top and dock at the bottom)

- I changed the settings so that the bultin display of the macbook was always the "main" display (using the system preferences option for displays and dragging the menu bar over onto the icon for the macbook builtin display)

- With it set so the macbook's builtin display is always the "main" display it will now connect to external displays with and without the magsafe power adapter being connected- problem solved.

I think there is a bug here and it should be fixed.