We had the same problem with Youtube links. It's the IPB media tag that causes this problem. There's no option to disable it only in the shoutbox. What we did with Youtube was that we removed the media tag for this, since there's a bbcode for that anyway. And we can only disable it globally which causes other stuff to break too. So it's still unsolved, the only possibility would be to do a bbcode vimeo player for example. There's also a soundcloud media tag, it's the only work for this one to work, it caused a conflict as bbcode and didn't work.