This is now fixed. It will reject all links with an html content type in its header that doesn't match a trusted source. This breaks a few things, but it can't be helped for now. The idea was you could provide a link to an imgur page for example and it'd parse that into a media link, but it will reject this now since it's more strict. Will review adding more trusted sources in the future, but for now html links are only accepted from youtube and vimeo.