I am also having issues with WordPress 3.5 and attaching images to pages and posts.
When i try to attach an image to the page or post through the ‘Add Media’ button the image does not show in my gallery on the front end.
It seemed though that when i am in the Media Library if i click the drop down menu and select ‘Uploaded to this page’ and then i move one of the images to second position and then put it back. From then on when i upload an image to be attached it then shows in the gallery.
I am not sure why this works. It seems to be something to do with the image not being assigned a menu order number unless i move one of the image’s positions.
