I looked at what you posted originally, and you used the wrong tags somehow on your link. There is noting wrong with posting youtube links on Bikeforums.

If your post comes out differently than you expect, I suggest editing it and clicking on the "source" button in the toolbar above the edit box. That way you can see what's going on. I think if you had just removed the incorrect tags, it would have parsed the url properly. A link will have "url" in square brackets.