Bibtex puts wrong reference name

Question

I'm using the style plainnat with the beamer class. I'm using BibTeX and this happens. I have the following in my .bib

@Article{ TiWuNg07,
    title = "{Performance analysis and improvement for BitTorrent-like file sharing systems}",
    author = "Y. Tian and Di Wu and KW Ng",
    journal = "Concurrency and Computation: Practice and Experience",
    volume = "19",
    number = "13",
    pages = "1811--1835",
    year = "2007",
    publisher = "John Wiley \& Sons"
}

And this is what appears as the bibitem:

\bibitem[Tian et~al.(2007)Tian, Wu, and Ng]{TiWuNg07}
Y.~Tian, Di~Wu, and KW~Ng.
\newblock {Performance analysis and improvement for BitTorrent-like file
  sharing systems}.
\newblock \emph{Concurrency and Computation: Practice and Experience},
  19\penalty0 (13):\penalty0 1811--1835, 2007.

Minimal code for .tex:

\documentclass[10pt,pdfpagelabels]{beamer}
\usepackage{tabulary}
\usepackage{snapshot}
\usepackage{todonotes}
\usefonttheme[onlymath]{serif}
\setbeamercovered{transparent=100}
\mode<presentation>
{
  \usetheme{Warsaw}
  \setbeamercovered{transparent}
}
\usepackage[spanish]{babel}
\usepackage[latin1]{inputenc}
\usepackage{lmodern}
\hypersetup{pdfnewwindow=true}

\begin{document}
\begin{frame}{Tian, Wu, Ng - 2007\cite{TiWuNg07}}
\end{frame}
\section{Referencias}
\begin{frame}[allowframebreaks]{Referencias}
\bibliographystyle{plainnat}
\bibliography{modelo}
\end{frame}
\end{document}

The citation appears as [Tian et~al.(2007)Tian, Wu, and Ng] when it should be [Tian et~al.(2007)]

As you can see, in the citation text, the authors appear again after the year. Why is this happening and how can I solve it without changing it manually? All the other bibitems appear correctly.

Answer 1

What makes you think that the plainnat style will work without the natbib package? ;-)

Add the following to your preamble (the second code line will make natbib compatible with beamer):

\usepackage{natbib}
\newcommand*{\newblock}{}

and use \citep instead of \cite in the document.

Answer 2

You are using the bibliography style plainnat, which is meant to be used with the natbib package, without actually loading this package. natbib stores some extra information, such as the author names and the year in the label. To get correct labels, either load natbib, or change the style to just plain.