For anyone that was using trunk which is the bleeding edge version of WordPress during 3.6 development you may have used a couple of new media fields that were added to the new Post Formats UI. Those fields along with the Post Formats UI were yanked from core. If you’d like to migrate the data within those fields back into the default post content so that it isn’t lost within the post meta, you’ll need to use the WordPress New Post Format UI Unmigrator plugin by Viper007Bond. You’ll need to download and then upload the new-post-format-unmigrator zip file to your website. Once installed and activated, browse to Tools – New Post Formats and if any posts need to be moved, they’ll be listed, and then automatically migrated.
Post Format UI Unmigrator