Since the multiwiki features were added, debugging is broken in Vagrant. If you try to use it, you get something like this:
This is in PHPStorm, maybe other IDEs are more clever, I don't know. But at the very least it is impossible to debug multiwiki issues since the PHP files under /var/www are not accessible from the host machine. Vagrant should put those files under /vagrant/docroot or something and symlink /var/www to that (or copy if symlinking is problematic although the ability to access and alter those files from an IDE would be nice).