This is an entirely different issue. This is a problem with the html of the website.
Keep in mind that most links to images, stylesheets, scripts used within vBulletin are relative to the forums path. So, if you want to output templates that link to images in your forums' directory using relative links, you can probably just add a
base href tag. Of course, having a link to your forums/custom page would make finding the cause of this small issue very easy.
Hope this helps!