Pandoc fails to escape initial % in markdown mode

[elliottslaughter]

Here's the initial input:

$ perl -e 'print "\n% title\n% author\n% date\n"'

% title
% author
% date

Note that the initial blank line means that the % title line will not actually be treated as the title, but will be a paragraph containing a % character. (Similarly for author and date.)

Now let's run this through Pandoc and back:

$ perl -e 'print "\n% title\n% author\n% date\n"' | pandoc -s -f markdown -t json | pandoc -s -f json -t markdown
% title % author % date

Note that the initial blank line is gone. If we do another pass through Pandoc:

$ perl -e 'print "\n% title\n% author\n% date\n"' | pandoc -s -f markdown -t json | pandoc -s -f json -t markdown | pandoc -s -f markdown -t json | pandoc -s -f json -t markdown
---
title: 'title % author % date'
---

It now gets interpreted as a title.

The bug is in the first conversion from JSON to Markdown. When producing a Markdown file which contains an initial paragraph that starts with %, either the % should be escaped or there should be a blank line at the start to avoid interpreting the % as a title.

$ pandoc --version
pandoc 1.19.2.1
Compiled with pandoc-types 1.17.0.4, texmath 0.9, skylighting 0.1.1.5