Having the same issue. It seems like what changed in the update was the way the system associates images with a post or page. Consider the following:
-Images are still there in the uploads – they just don’t show up as “attached” to the page
-The gallery code that was generated prior to the recent 3.5.1 update was simple, such as [gallery cols="4"] or something like that
-Galleries work, but the default behavior is to use ids and not attach photos to a particular page.
Nonetheless, I’m dealing with several broken galleries and would like to be able to fix this problem without having to manually go and redo EACH one.
Thanks to anyone who can offer advice on this issue we both are experiencing.