I’m running into this problem as well, and seem to have stumbled through a workaround. For reference, I’m using 2.8.1.
- Add new post.
- Manually type in
[gallery] into post form.
- Save draft.
- Upload pictures.
- Save all changes.
- Now you should see the option to insert the gallery into the post.
- Insert into post.
- Delete the second
[gallery] that appears in the post form.
It’s a pretty condensed list, but I think you get the idea that using the [gallery] shortcode seems to convince WP that you really want to attach the images to the post.