I found that removing the code from checkurl and parseurl erases the whole message if a link is anywhere in the message.
But your lead was not in vain... I was successfully able to disable "hotlinks" by simply changing the last line in the function checkurl from:
return "<a href=\"$righturl\" target=\"_blank\">".str_replace('\"', '"', $hyperlink)."</a>";
to:
return "<a =\"$righturl\" >".str_replace('\"', '"', $hyperlink)."</a>";
now when I type
www.test.com in the message or use the
http:// button in the vbcode area the url appears as text not a hotlink.