Howdy - It doesn't seem like you're missing anything here. Are you able to explain in detail, or upload a screenshot, of where in Game Center this is happening? High frequency images (think tree branches, text, lots of sharp edges) can scale poorly as well. Does this sound like the image you're using?

Posting as a reply as well since my original post as a comment was an error :) Hi ddunham, I enjoyed chatting with you at WWDC. While I can't comment on when it will be released, this issue has been fixed such that reporting 0% on hidden achievements causes them to become visible. While we'll likely preserve this behavior going forward there are plans to expose a proper "reveal" API in the future as well. Thanks again for the feedback here.