pgfplots 3D surface broke

Question

I'm a newcomer to LaTeX and pgfplots. And now I found a problem while I was using \addplot3. It seems that the image behaved abnormally on perspective.This is the image generated.

For reference I changed to view={20}{0}, and it became the image below.

Could anyone tell me how to deal with it, please? I don't know how to make the first image right. My tex code is

%!TEX program = xelatex
\documentclass{article}
\usepackage{fontspec, xunicode, xltxtra, pgfplots}  
\setmainfont{Hiragino Sans GB}  
\pgfplotsset{compat=1.8}

\title{Title}
\author{}

\begin{document}

\begin{figure}
\centering
\begin{tikzpicture}
    \begin{axis}[
title={$x \exp(-x^2-y^2)$},
xlabel=$x$, ylabel=$y$,
small,
view={20}{30}
] \addplot3[surf,mesh/cols=50,domain=-2:2,domain y=-1.3:1.3]
            table {2.dat};
    \end{axis}
\end{tikzpicture}
\caption{a small example}
\end{figure}

\end{document}

THANKS!

Answer 1

As suggested in the comments, use the option z buffer = sort to correct the sorting in the data file. If you plot the function directly in pgfplots, the problem does not exist....

\documentclass{article}
\usepackage{pgfplots}  
\pgfplotsset{compat=1.8}


\begin{document}

\begin{figure}
\centering
\begin{tikzpicture}
    \begin{axis}[
title={$x \exp(-x^2-y^2)$},
xlabel=$x$, ylabel=$y$,
small,
view={20}{20}
] 
\addplot3[surf,domain=-2:2,domain y=-2:2,samples=50]
           {x*exp(-x*x-y*y)} ;
    \end{axis}
\end{tikzpicture}
\caption{a small example}
\end{figure}

\end{document}