V1.5 “comment_url” filter

I can’t make it work ??

I’ve written (most of) a plugin and the “comment_text” filter is working perfectly, but “comment_url” for some reason does not return the URL of the comment poster, and WP appears to ignore any text I return from the function.

Anyone know if this has changed in 1.5? No one seems to have updated the codex with all the filter hooks yet, and there were never any descriptions. Am I even using the right thingy?