Are you sure this works with individual pages/posts in 3.5? I’m not seeing anything on the right side when I select images in the media gallery: http://prntscr.com/opwoo. Those items you see were all uploaded directly to that page. I have attached media to this page using the media library using your attach function, and they show as attached there, but don’t actually seem to be attached to the page here. I can provide screenshots off line if you like. They are private pages. Thanks.
The attached media will display if you are using the gallery short code if you are using some other method like a plugin or theme template you have to use the custom functio to display the media. For more information read the FAQ page