The weirdness I experience: neither Retrobatch nor Acorn seems to be able to detect the transparency around the actual motive. Acorn gives me this message at least: “No transparent Edges”.
Can you tell me what versions of Acorn and Retrobatch you’re using? I tried out the attached image in both, and the size went from 604x726 to 596x719. (Using Retrobatch 1.2 beta as well as Acorn 6.3.2). Are you using the exact image that you uploaded? And if you download that image from http://forums.flyingmeat.com/uploads/db3784/03ed16da1890d4042cb940bb0d986e707942a8c7 does it work as expected? I’m wondering if maybe some post processing was going on with the version I grabbed.