Only uploaded attachments…

Hello!
I’m not able to insert previously uploaded files from the Media Library directly into the topic / reply, but when I choose to upload a file from the desktop, the “insert into post” button is enabled. I’m running WP 4.2.2 with the Buddy Theme.
Has anyone seen this before? I’ve got most of the site’s plugins disabled for debugging this and it’s hopefully not that complicated to solve… Any ideas?

https://wordpress.org/plugins/bbpress-enable-tinymce-visual-tab/