I've recently updated to Wordpress 3.5, everything works fine and the new Media Uploader looks great. However when I add an image gallery to a post or page it won't show up on the render html page, but it will still be there in the editor!
I'm using a custonized Roots theme, maybe it has to do with that and not with Wordpress at all. The images are not being in stored in wp-content/uploads, but in a folder called assets on the root level, but I don't think this should be an issue since there is no problem with inserting single images into a post, only with galleries apparently.