Are you using the sitemap generation in XF? Do you have content titles enabled in URLs? Are all of your URLs indexed like this or just some? Do you have an example of URLs which are being indexed like this?
I would be expecting Google to index what it gets to after the final redirection.
That being said, I'm pretty sure the Sitemap generation will eventually put this right, and eventually the vBulletin redirects will be less relevant as your new site gets indexed normally.