WordPress version 3.9.1 is a maintenance release and is now available for download. (This release fixes 34 bugs.) If you have not updated (or are not set up for automatic background updates) – take some time to backup your site and update.
You can read more about the update: http://core.trac.wordpress.org/query?status=closed&group=resolution&milestone=3.9.1
You can download WordPress 3.9.1: http://wordpress.org/wordpress-3.9.1.zip