comment causes [package error]

Question

I want to export an org file containing a tikz diagram to pdf.
I've read the manual. This is the most minimal example I could come up with:

#+LATEX_HEADER: \usepackage{tikz}

#+begin_src emacs-lisp :results silent
(org-babel-do-load-languages
 'org-babel-load-languages '((latex . t)))
  (setq org-babel-latex-htlatex "htlatex")
  (defmacro by-backend (&rest body)
    `(case (if (boundp 'backend) (org-export-backend-name backend) nil) ,@body))
#+end_src

#+header: :file (by-backend (html "tree.svg") (t 'nil))
#+header: :imagemagick
#+header: :results (by-backend (pdf "latex") (t "raw"))
#+begin_src latex
  \begin{tikzpicture} %foo
    \draw[thin] (0,0) circle (1);
    %\draw (ba) circle (1);  
  \end{tikzpicture}
#+end_src

To execute I put the cursor in the elisp block and do C-c C-c, then M-x org-latex-export-to-pdf

This yields:

Process completed with errors: [package error]

Interestingly it works when I remove just one of the 2 comments (or replace ba by 0,0)

Upon doing M-x org-latex-export-to-latex I can see that the code block evaluates to

\begin{tikzpicture} \%foo
  \draw[thin] (0,0) circle (1);
  \%\draw (ba) circle (1);    
\end{tikzpicture}

The comments aren't ignored but the % are escaped! (And the package error is probably how latex deals with unknown tokens foo and ba)

How can I keep the comments in my code and still compile?

Org-mode version 8.2.10
GNU Emacs 25.2.2

Progress:
jagrg is correct I don't get the error with emacs -Q.
I have now 2 types of errors:

emacs -Q --load debug_init

1) With debug_init being either of the following files:

(require 'package)
(add-to-list 'load-path "/usr/share/emacs25/site-lisp/mu4e")
(require 'mu4e)
--- or ---
;;(require 'package)
(add-to-list 'load-path "/usr/share/emacs25/site-lisp/mu4e")
(require 'mu4e)

results in Process completed with errors: [package error] and If I remove %foo it compiles. (I can also just fix up the generated .tex file)

2) with emacs -Q or either of the following init files:

(require 'package)
;;(add-to-list 'load-path "/usr/share/emacs25/site-lisp/mu4e")
;;(require 'mu4e)
--- or ---
(require 'package)
(add-to-list 'load-path "/usr/share/emacs25/site-lisp/mu4e")
;;(require 'mu4e)

I get by-backend: Symbol’s function definition is void: case

Update 2 Symbol’s function definition is void is solved, thanks jagrg!

current setup:

myinit:

(require 'cl-lib)                                                                                           
(org-babel-do-load-languages                                                                                
 'org-babel-load-languages '((latex . t)))                                                                  
(setq org-babel-latex-htlatex "htlatex")                                                                  
(defmacro by-backend (&rest body)                                                                         
 `(cl-case (if (boundp 'backend) 
               (org-export-backend-name backend) nil) ,@body))   

main.org:

#+LATEX_HEADER: \usepackage{tikz}
#+header: :file (by-backend (html "tree.svg") (t 'nil))
#+header: :imagemagick
#+header: :results (by-backend (pdf "latex") (t "raw"))
#+begin_src latex
  \begin{tikzpicture} %foo
    \draw[thin] (0,0) circle (1);
    %\draw (ba) circle (1);  
  \end{tikzpicture}
#+end_src

open with emacs -Q --load myinit main.org then type M-x -l-pd resulting in Process completed with errors: [package error]

Update 3
changing "raw" to "results" does the trick.

Answer 1

FWIW I cannot reproduce your problem. The %foo comment should not be escaped so there's definitely something wrong, either with your configuration or a bug with your version of Org. I would try with emacs -Q first and if it still fails I would try upgrading Org. You could also check for errors in the compilation buffer.