Site being redirected to youtube after posting youtube video shortcode

When I use the youtube video shortcode in the editor my site redirects to the youtube homepage.

Any reason for this?

I do not have any plugins ACTIVE that involve youtube.

I thought the video shortcodes were part of TinyMCE Advanced. Maybe they are part of the Wp general editor?

I disabled TinyMCE Advanced but the shortcode option is still there and it still redirects.

I can stop it from redirecting by removing the shortcode for the video from the page.
Thanks
iso.