ob-shell: async support in "shell" vs "bash"

[Suhail Singh]

On my system both "shell" and "bash" language blocks use "bash" as
checked by:

    #+begin_src shell :results replace
      cat /proc/$$/comm
    #+end_src

    #+RESULTS:
    : bash

    #+begin_src bash :results replace
      cat /proc/$$/comm
    #+end_src

    #+RESULTS:
    : bash

However, the value of org-babel-header-args:lang differs:

    #+begin_src emacs-lisp :results value replace verbatim
      org-babel-header-args:shell
    #+end_src

    #+RESULTS:
    : ((async (yes no)))

    #+begin_src emacs-lisp :results value replace verbatim
      org-babel-header-args:bash
    #+end_src

    #+RESULTS:
    : nil

Is this a bug, or are async blocks only currently allowed in "shell"
language blocks and not "bash" language blocks?

-- 
Suhail