Because your post has both URL and U2B tags.
When using the U2B tags, you only need to put the part of the youtube link after the '=' sign. So, for instance, with your video, you only need to put the "4-jcmyTyogw" part of the video link between the [u2b] and the [ /u2b] tags. There's no need to use the URL tag for a youtube video
