I have found out how this problem has seeped into ASDF --- ASDF-INSTALL, at least the version I have (I am checking now to see if there's an improved version) --- seeds asdf:*central-registry* with pathnames with :name = "". This is done by the directorify function in installer.lisp.
Investigating further.
Perhaps this behavior should simply be stamped out of ASDF-install....