My office is in a bit of a rush right now, it's easy to miss such simple thing like that
Thanks for the hint Eduardo!
by the way, my colleague was doing that in order to get a higher resolution of exported image from the 3D window, it worked but the image proportion was constrained to a somewhat very wide aspect ratio even though "keep proportion" option was already turned on
the width was fine and could have quite a reasonable pixel length but the height seemed to be limited by the height of the monitor's resolution, any idea?
-John