node not appearing when used with pos option in a pgfplot [closed]

Question

I want to place a node on a plot using the pathway modifier: node[pos=0.5] {node text};. The pgfplots manual clearly describes how that is done, but my node doesn't appear. Could my scaling be a problem here (it is applied by the input filter style)?

\documentclass{article}
\usepackage[a2paper,landscape,margin=1cm]{geometry}

\usepackage{tikz,pgfplots}
\pgfplotsset{compat=1.5}

\pgfmathsetmacro{\smin}{4000}
\pgfmathsetmacro{\smax}{9200}
\pgfmathsetmacro{\hmin}{2000}
\pgfmathsetmacro{\hmax}{3900}

\pgfplotstableset{input filter/.style ={y expr=\thisrowno{1}/1e3}}

\begin{document}
\pagestyle{empty}
  \noindent\begin{tikzpicture}
    \begin{axis}[xmin=\smin,xmax=\smax,width=52cm,
                  ymin=\hmin,ymax=\hmax,height=38cm,
                  scale only axis,
                  major tick length={0pt},
                  minor tick length={0pt},
                  xticklabel={\pgfmathparse{\tick/1e3}\pgfmathresult},
                  yticklabel={\pgfmathparse{\tick}\pgfmathresult},
                  axis lines*=none
                  ]
      \addplot table[input filter] {
        5575.75757575757575779 2010304.18052640024086
        6311.11111111111111116 2284412.95212492412338
        7886.86868686868686851 2900069.5315761277061
        9200 3795110.22478821340428
      } node[pos=0.5] {asdf};
    \end{axis}
  \end{tikzpicture}\\
\end{document}

I've also tried to place the node using the decorations.markings library:

\usetikzlibrary{decorations.markings}
\addplot[postaction={decorate},
         decoration={markings,mark=at position 0.5 with \node {asdf};}
        ] table[input filter] {
  5575.75757575757575779 2010304.18052640024086
  6311.11111111111111116 2284412.95212492412338
  7886.86868686868686851 2900069.5315761277061
  9200 3795110.22478821340428
};

and the node didn't appear as well. Other position settings such as at position 1cm also didn't place a node on the plot.