Now click on the last 'folder' (?) which should be the link to the same page. In the above example, it is "Other languages". It expects a base HREF and tries to visit a web-site http://forums/listCategory/11.
The same can be seen in other similar 'sibling' web-pages (e.g., replace the 11 after http://www.coderanch.com/forums/c/ with some other number such as 1 or 4 or 13). Only, in the example I gave, there is a forum (child) with the same name as the group (parent) viz., "Other languages", so it wasn't entirely stupid of me to be clicking it. At least that is my excuse for stumbling on to the bug.
(I've deliberately avoided HTML so as to not let casual visitors click on those links).
"Perfection is achieved, not when there is nothing more to add, but when there is nothing left to take away." -- Antoine de Saint-Exupery
author and iconoclast