[O] Bug: html-preamble doesn't work with a function [8.3.2 (8.3.2-39-gd537a3-elpa @ /home/pillow/.emacs.d/elpa/org-20151123/)]

[Pillow Kuda Sai]

My setup:
;;; Minimal setup to load latest 'org-mode'
;; activate debugging
(setq debug-on-error t
      debug-on-signal nil
      debug-on-quit nil)

;; add latest org-mode to load path
(add-to-list 'load-path (expand-file-name "~/.emacs.d/elpa/org-20151123/"))
(add-to-list 'load-path (expand-file-name
"~/.emacs.d/elpa/org-20151123/" t))

What I did:
(require 'ox-publish)
(setq org-publish-project-alist
      '(
        ("org-notes"
         :base-directory "~/org/"
         :base-extension "org"
         :publishing-directory "~/public_html/"
         :recursive t
         :publishing-function org-html-publish-to-html
         :headline-levels 4             ; Just the default for this project.
         :auto-preamble t
         ;; :html-preamble "Howdy" ; does work
         :html-preamble (concat "Howdy")
         )
        ("org-static"
         :base-directory "~/org/"
         :base-extension "css\\|js\\|png\\|jpg\\|gif\\|pdf\\|mp3\\|ogg\\|swf"
         :publishing-directory "~/public_html/"
         :recursive t
         :publishing-function org-publish-attachment
         )
        ("org" :components ("org-notes" "org-static"))))

What I expected: All off the above code is from
http://orgmode.org/worg/org-tutorials/org-publish-html-tutorial.html
except for the :html-preamble part. I want to add my own preamble by
using a function. :html-preamble sets org-html-preamble (the options
are: nil, t, string, function that must return a string). When using a
string (:html-preamble "Howdy") it works. When using a function that
returns a string (:html-preamble (concat "Howdy")) it doesn't work.

I'm not entirely sure if this is a bug or if I'm missing something but
hopefully the mailing-list can help me out :)

Thanks in advance, Pillow
------------------------------------------------------------------------



Emacs  : GNU Emacs 25.0.50.2 (x86_64-unknown-linux-gnu, GTK+ Version 3.14.5)
 of 2015-10-09
Package: Org-mode version 8.3.2 (8.3.2-39-gd537a3-elpa @
/home/pillow/.emacs.d/elpa/org-20151123/)

current state:
==============
(setq
 org-src-lang-modes '(("ocaml" . tuareg) ("elisp" . emacs-lisp) ("ditaa"
. artist) ("asymptote" . asy)
                      ("dot" . fundamental) ("sqlite" . sql) ("calc" . 
fundamental)
("C" . c) ("cpp" . c++)
                      ("C++" . c++) ("screen" . shell-script))
 org-tab-first-hook '(org-hide-block-toggle-maybe
org-src-native-tab-command-maybe
                      org-babel-hide-result-toggle-maybe 
org-babel-header-arg-expand)
 org-sparse-tree-default-date-type 'scheduled-or-deadline
 org-latex-default-packages-alist '(("AUTO" "inputenc" t) ("T1"
"fontenc" t) ("" "fixltx2e" nil) ("" "graphicx" t)
                                    ("" "longtable" nil) ("" "float" nil) ("" 
"wrapfig" nil) (""
"rotating" nil)
                                    ("normalem" "ulem" t) ("" "amsmath" t) ("" 
"textcomp" t) (""
"marvosym" t)
                                    ("" "wasysym" t) ("" "amssymb" t) ("" 
"hyperref" nil)
"\\tolerance=1000")
 org-speed-command-hook '(org-speed-command-default-hook
org-babel-speed-command-hook)
 org-occur-hook '(org-first-headline-recenter)
 org-metaup-hook '(org-babel-load-in-session-maybe)
 org-html-format-drawer-function '(lambda (name contents) contents)
 org-clock-into-drawer nil
 org-latex-format-inlinetask-function 'ignore
 org-confirm-shell-link-function 'yes-or-no-p
 org-ascii-format-inlinetask-function 'org-ascii-format-inlinetask-default
 org-latex-text-markup-alist '((bold . "\\textbf{%s}") (code . verb)
(italic . "\\emph{%s}")
                               (strike-through . "\\sout{%s}") (underline . 
"\\uline{%s}")
                               (verbatim . protectedtexttt))
 org-latex-format-headline-function
'org-latex-format-headline-default-function
 org-after-todo-state-change-hook '(org-clock-out-if-current)
 org-latex-format-drawer-function '(lambda (name contents) contents)
 org-src-mode-hook '(org-src-babel-configure-edit-buffer
org-src-mode-configure-edit-buffer)
 org-agenda-before-write-hook '(org-agenda-add-entry-text)
 org-babel-pre-tangle-hook '(save-buffer)
 org-html-allow-name-attribute-in-anchors t
 org-latex-logfiles-extensions '("aux" "idx" "log" "out" "toc" "nav"
"snm" "vrb")
 org-export-copy-to-kill-ring 'if-interactive
 org-mode-hook '(#[nil "\300\301\302\303\304$\207"
                   [org-add-hook change-major-mode-hook org-show-block-all 
append
local] 5]
                 #[nil "\300\301\302\303\304$\207"
                   [org-add-hook change-major-mode-hook 
org-babel-show-result-all
append local] 5]
                 org-babel-result-hide-spec org-babel-hide-all-hashes)
 org-archive-hook '(org-attach-archive-delete-maybe)
 org-ascii-format-drawer-function '(lambda (name contents width) contents)
 org-ctrl-c-ctrl-c-hook '(org-babel-hash-at-point
org-babel-execute-safely-maybe)
 org-cycle-hook '(org-cycle-hide-archived-subtrees
org-cycle-hide-drawers org-cycle-hide-inline-tasks
                  org-cycle-show-empty-lines 
org-optimize-window-after-visibility-change)
 org-html-mathjax-template "<script type=\"text/javascript\"
src=\"%PATH\"></script>\n<script
type=\"text/javascript\">\n<!--/*--><![CDATA[/*><!--*/\n
MathJax.Hub.Config({\n        // Only one of the two following lines,
depending on user settings\n        // First allows browser-native
MathML display, second forces HTML/CSS\n        :MMLYES: config:
[\"MMLorHTML.js\"], jax: [\"input/TeX\"],\n        :MMLNO: jax:
[\"input/TeX\", \"output/HTML-CSS\"],\n        extensions:
[\"tex2jax.js\",\"TeX/AMSmath.js\",\"TeX/AMSsymbols.js\",\n
        \"TeX/noUndefined.js\"],\n        tex2jax: {\n
inlineMath: [ [\"\\\\(\",\"\\\\)\"] ],\n            displayMath: [
['$$','$$'], [\"\\\\[\",\"\\\\]\"],
[\"\\\\begin{displaymath}\",\"\\\\end{displaymath}\"] ],\n
skipTags:
[\"script\",\"noscript\",\"style\",\"textarea\",\"pre\",\"code\"],\n
        ignoreClass: \"tex2jax_ignore\",\n            processEscapes:
false,\n            processEnvironments: true,\n            preview:
\"TeX\"\n        },\n        showProcessingMessages: true,\n
displayAlign: \"%ALIGN\",\n        displayIndent: \"%INDENT\",\n\n
  \"HTML-CSS\": {\n             scale: %SCALE,\n
availableFonts: [\"STIX\",\"TeX\"],\n             preferredFont:
\"TeX\",\n             webFont: \"TeX\",\n             imageFont:
\"TeX\",\n             showMathMenu: true,\n        },\n
MMLorHTML: {\n             prefer: {\n                 MSIE:
\"MML\",\n                 Firefox: \"MML\",\n                 Opera:
\"HTML\",\n                 other:   \"HTML\"\n             }\n
}\n    });\n/*]]>*///-->\n</script>"
 org-html-mathjax-options '((path
"http://orgmode.org/mathjax/MathJax.js";) (scale "100") (align "center")
                            (indent "2em") (mathml nil))
 org-export-with-creator 'comment
 org-html-creator-string "<a
href=\"http://www.gnu.org/software/emacs/\";>Emacs</a> 25.0.50.2 (<a
href=\"http://orgmode.org\";>Org</a> mode 8.2.10)"
 org-latex-with-hyperref "\\hypersetup{\n pdfauthor={%a},\n
pdftitle={%t},\n pdfkeywords={%k},\n pdfsubject={%d},\n pdfcreator={%c},
\n pdflang={%L}}\n"
 org-timer-default-timer 0
 org-babel-process-comment-text 'org-babel-trim
 org-babel-tangle-lang-exts '(("emacs-lisp" . "el"))
 org-confirm-elisp-link-function 'yes-or-no-p
 org-metadown-hook '(org-babel-pop-to-session-maybe)
 org-latex-listings-langs '((emacs-lisp "Lisp") (lisp "Lisp") (clojure
"Lisp") (c "C") (cc "C++")
                            (fortran "fortran") (perl "Perl") (cperl "Perl") 
(python
"Python") (ruby "Ruby")
                            (html "HTML") (xml "XML") (tex "TeX") (latex 
"[LaTeX]TeX")
(shell-script "bash")
                            (gnuplot "Gnuplot") (ocaml "Caml") (caml "Caml") 
(sql "SQL")
(sqlite "sql"))
 org-effort-durations '(("h" . 60) ("d" . 480) ("w" . 2400) ("m" . 9600)
("y" . 96000))
 org-html-format-headline-function 'ignore
 org-structure-template-alist '(("s" "#+BEGIN_SRC ?\n\n#+END_SRC" "<src
lang=\"?\">\n\n</src>")
                                ("e" "#+BEGIN_EXAMPLE\n?\n#+END_EXAMPLE" 
"<example>\n?\n</example>")
                                ("q" "#+BEGIN_QUOTE\n?\n#+END_QUOTE" 
"<quote>\n?\n</quote>")
                                ("v" "#+BEGIN_VERSE\n?\n#+END_VERSE" 
"<verse>\n?\n</verse>")
                                ("V" "#+BEGIN_VERBATIM\n?\n#+END_VERBATIM" 
"<verbatim>\n?\n</verbatim>")
                                ("c" "#+BEGIN_CENTER\n?\n#+END_CENTER" 
"<center>\n?\n</center>")
                                ("l" "#+BEGIN_LaTeX\n?\n#+END_LaTeX" "<literal
style=\"latex\">\n?\n</literal>")
                                ("L" "#+LaTeX: " "<literal 
style=\"latex\">?</literal>")
                                ("h" "#+BEGIN_HTML\n?\n#+END_HTML" "<literal
style=\"html\">\n?\n</literal>")
                                ("H" "#+HTML: " "<literal 
style=\"html\">?</literal>")
                                ("a" "#+BEGIN_ASCII\n?\n#+END_ASCII" "") ("A" 
"#+ASCII: " "")
                                ("i" "#+INDEX: ?" "#+INDEX: ?")
                                ("I" "#+INCLUDE: %file ?" "<include file=%file 
markup=\"?\">"))
 org-export-creator-string "Emacs 25.0.50.2 (Org mode 8.2.10)"
 org-html-format-inlinetask-function 'ignore
 org-clock-out-hook '(org-clock-remove-empty-clock-drawer)
 org-src-fontify-natively nil
 org-publish-project-alist '(("org-notes" :base-directory "~/org/"
:base-extension "org" :publishing-directory
                              "~/public_html/" :recursive t :publishing-function
org-html-publish-to-html
                              :headline-levels 4 :auto-preamble t 
:html-preamble (concat
"Howdy"))
                             ("org-static" :base-directory "~/org/" 
:base-extension
                              
"css\\|js\\|png\\|jpg\\|gif\\|pdf\\|mp3\\|ogg\\|swf"
:publishing-directory
                              "~/public_html/" :recursive t :publishing-function
org-publish-attachment)
                             ("org" :components ("org-notes" "org-static")))
 )