1. Meant redactor, sorry. I use TinyMCE for my webdev, and thought that XenForo was using it, too.
2. I could reproduce it here, on xenforo.com
3. To reproduce,
When typing a reply, click the "Insert image" icon[1], type this URL: http://j.ungeek.eu/FFVWHfj and insert.
What it does, here, on...