There might be a separate dialog box when rendering from your art program that can change your resolution. When I use Flash I can set the document to a certain size (640 x 400, for example), but then when I export (the equivalent of rendering) the graphic as a PNG a dialog comes up that can change the final resolution (optional dpi, etc.). If these numbers get changed they tend to persist (ie not default back to original settings) and it can throw all my art out of whack. Something to check anyway, since it seems as if you think your draw program is changing the resolution on you.