[O] Python source block and :dir header arg

[Joao Cortes]

Consider the following python source block,
           
#+begin_src python :results output : session :dir ./run
        import os;
        cwd = os.getcwd()
        print(cwd)
#+end_src

The dir header arg should change the directory used to run the session,
in this case to the directory "../base/run", where "base" is the parent
directory the file visited by the current buffer. Instead, I get
"../base". Is this a bug?

Thank you
Joao Cortes