Let me add that when not specifying ":results verbatim", the presence of
the % sign in the output also triggers table formatting:

#+BEGIN_SRC sh :session *session*
echo "a%b"
#+END_SRC

#+RESULTS:
|   |
| b |


Whereas without session, the output is formatted like this

#+BEGIN_SRC sh
echo "a%b"
#+END_SRC

#+RESULTS:
: a%b


And if the session has not been opened already, then the first time
evaluation does not cut off the results:

#+BEGIN_SRC sh :session *session2*
echo "a%b"
#+END_SRC

#+RESULTS:
|     |
| a%b |


greetings, Til

Emacs : GNU Emacs 25.1.1 (x86_64-unknown-linux-gnu, GTK+ Version 3.22.7) of 2017-02-07
Package : Org mode version 9.0 (9.0-elpa @ /home/tils/.emacs.d/elpa/org-20161102/)