The sentences following that statement in the hdiutil manual are also helpful: "The image filesystem currently only behaves this way as a result of a direct at

The sentences following that statement in the hdiutil manual are also helpful: "The image filesystem currently only behaves this way as a result of a direct attach action and will not behave this way if, for example, the filesystem is unmounted and remounted. Moving the image file to a different volume with sufficient free space will allow the image's filesystem to grow to its full size." hdiutil has some of the best man pages I've ever run across.