If a custom profile field is designed to hold a URL, that URL is parsed into an "<a href" link anchor when the VALUE is passed to the template in viewtopic_body and memberlist_view. This preformatted anchor, complete with html comments, cannot be used in a user-formatted link, such as if they wanted to include an image or such.

For instance, when I type "www.google.com" into my profile field, it is parsed to "<!-- w -><a class="postlink" href="http://www.google.com">www.google.com</a><!- w -->" in the PROFILE_fieldname_VALUE, so I cannot format the URL as I like in memberlist_view or viewtopic_body.