I just posted some youtube links and the HTML didn't translate to the screen. I run a PHPBB board and I'm pretty sure the problem lays with how the admin configures the HTML settings.
In the admin control panel, one option is what HTML tags are acceptable. I think i, b and img are kind of the standars, but you can add "a" or "a href" so that clickable links are clickable!
Just a suggestion!
Jo