Persisting the current working directory in an org-babel session

[Adam Sneller]

For some reason, I am unable to make changes to my working directory persist, 
from one emacs-lisp SRC block to the next.

For example, consider the following:

        * Literate programming in a single session
        :PROPERTIES:
        :header-args: :var DIR="/Users/adam/Desktop/test"
        :END:

        #+BEGIN_SRC emacs-lisp :session *elisp*
        (cd DIR)
        #+END_SRC

        #+RESULTS:
        : /Users/adam/Desktop/test/


        #+BEGIN_SRC emacs-lisp :session *elisp*
        (cd ".")
        #+END_SRC

        #+RESULTS:
        : /Users/adam/org/

The :header-args: define a starting directory (DIR="/Users/adam/Desktop/test"). 
The first block establishes the *elisp* session and navigates into DIR, using 
(cd DIR). Confirmation is then seen in the #+RESULTS. 

A second block is then created in the same *elisp* session. This simply echos 
the current working directory with (cd "."). BUT... the #+RESULTS show that the 
working directory has not persisted from our first block and has instead, 
defaulted to the default org-mode directory.

Now, I realise that I could have used :dir in my initial :header-args: to set 
the same working directory for all blocks. But what I am interested in is why 
my changes are not persisting, when (if I am not mistaken) this is the entire 
point of establishing a session?

Thanks!

Adam Sneller