finally I found the problem: it was not at all related to org or babel,
but due to a function in my ess-send-input-hook.
sorry for bothering :)
Thomas Alexander Gerds writes:
> still a beginner, and maybe therefore, in my setup (release is:
> 7.8.03,
> emacs 23.2.1) the following occurs
>
> -
When executing your example below on my system both code blocks work as
shown below.
#+begin_src R :results output :exports results
foo=matrix(1:2)
foo
#+end_src
#+RESULTS:
: [,1]
: [1,]1
: [2,]2
#+begin_src R :results output :exports results :session *R*
foo=matrix(3:8)
foo
still a beginner, and maybe therefore, in my setup (release is: 7.8.03,
emacs 23.2.1) the following occurs
-org.snip---
* here it works: org-ctrl-c-ctrl-c and export
#+begin_src R :results output :exports results
foo=matrix(1:2)
foo
#+end_src
#+RESULTS:
: