@{} and p{<length>} in latex tabular not parsed correctly

[njbart]

Example:

\documentclass{article}
\begin{document}

\begin{tabular}{ccc}
foo & bar & baz \\
foo & bar & baz
\end{tabular}

\begin{tabular}{@{}ccc@{}}
foo & bar & baz \\
foo & bar & baz
\end{tabular}

\begin{tabular}{p{20mm}p{20mm}p{20mm}}
foo & bar & baz \\
foo & bar & baz
\end{tabular}

\end{document}

Actual output:

$ pandoc -t markdown tabular.tex 
  ----- ----- -----
   foo   bar   baz
   foo   bar   baz
  ----- ----- -----

<span>@ccc@</span> foo & bar & baz\
foo & bar & baz

<span>p<span>20mm</span>p<span>20mm</span>p<span>20mm</span></span> foo
& bar & baz\
foo & bar & baz

Expected output:

  ----- ----- -----
   foo   bar   baz
   foo   bar   baz
  ----- ----- -----

for all three.