I don't see how this is a bug, that is how /drawsave is supposed to work, if you make a picture window that is 500x400 and then use /drawsave on that same window, the image file will be 500x400...
Two solutions for this can be:
1.) Make the picture window the same size as the image you're displaying.
2.) Use MDX to dock the picture window directly to the dialog, no need for /drawsave
