setting an org mode property header doesn't work for the first one

Question

I cannot seem to set #+PROPERTY: header-args:R as the first value and have it work the way I expect it to. This is used as an example for org-mode here.

Setting a language specific property for :exports works. (I've put in some emacs-lisp source blocks, and those results do not get shown.

Providing a name for the session does not change the output (i.e. :session *R*)

Changing the order just makes the first one not work.

(As an aside, how can I check what a #+PROPERTY is set to?)

org-mode 8.3.3 from elpa package. emacs-version 24.5.1 on OSX.

Some minimally working examples follow.

---

This works:

#+PROPERTY: header-args :session
#+PROPERTY: header-args:R :exports both

#+BEGIN_SRC R 
x = 3
#+END_SRC

#+BEGIN_SRC R 
x
#+END_SRC

resulting in:

x = 3
3
x
3

Also this works

#+PROPERTY: header-args :exports both
#+PROPERTY: header-args:R :session

#+BEGIN_SRC R 
x = 3
#+END_SRC

#+BEGIN_SRC R 
x
#+END_SRC

and results in the same results as above.

---

This does not work:

#+PROPERTY: header-args:R :session
#+PROPERTY: header-args:R :exports both

#+BEGIN_SRC R 
x = 3
#+END_SRC

#+BEGIN_SRC R 
x
#+END_SRC

resulting in:

x = 3
3
x

Also does not work

#+PROPERTY: header-args:R :exports both
#+PROPERTY: header-args:R :session

#+BEGIN_SRC R 
x = 3
#+END_SRC

#+BEGIN_SRC R 
x
#+END_SRC

resulting in:

x = 3
x

Answer 1

Add a + to the key to append values to a property.

For an instance, in your last example you should write:

#+PROPERTY: header-args:R :exports both
#+PROPERTY: header-args:R+ :session

Note the + behind the key header-args:R in the second line.

See the example

 #+PROPERTY: var  foo=1
 #+PROPERTY: var+ bar=2

in the orgmode online help http://orgmode.org/manual/Property-syntax.html.

Note, I wonder myself how the header-args:c++ property can be set without appending;-).