When I drag 'My iPhone App' application's file into iTunes it has proper view. Rounded corners and transparent background.
Then I close iTunes and open it again. Corners are still rounded but... What has happened with the background?
http://www.freeimagehosting.net/uploads/15fee337bc.png
Icon is a project's resource file named 'iTunesArtwork' with dimension 512x512, PNG format.