[Zope] URL is missing up in Zope

I've noticed that sometimes as I traverse my Zope sight the URL keeps growing.. For instance The main folder has an index_html mainfolder->index_html A subfolder doesn't mainfolder/subfolder If the index_html is accessed from the sub you get the mainfolders index_html as I expect to. However if I traverse the two folders sometimes the URL looks like mainfolder/subfolder/subfolder/subfolder/index_html Why.. Thanks