When one tries to paste links into YouTube comments, one is forbidden to use “http” or “www” in the comment-at all. Thus, one must use the root URL only. The problem with this, however, is that YouTube randomly intersperses invisible dashes into your link. Thus, one must first insert the link into a text editor (for Windows, Notepad) or word processor (MS Word, “Keep Text Only”, apparently the default setting in OpenOffice) to check for the hidden extra dashes. It’s easier in OpenOffice, as it highlights them.
UPDATE, 8 hours later:
Nah, still doesn’t work. YouTube corrupts those links anyway.