This is not really a bug. The software is automatically changing resource references between domain.com <--> wiki.domain.com to avoid browser security warnings. This can result in 404 errors if the forum and the wiki don't have the same base directory. This can't really be "fixed" on the software side because then there are situations where it won't work in the opposite direction.
On your server, create the directory wiki.domain.com/vb as a symlink that points to the directory containing domain.com/vb