Frage zu Footnote in Beamer Class in titlepage

\documentclass[xcolor=dvipsnames]{beamer}
\makeatletter
\mode<presentation>
{
  \usetheme{Berlin}      
  \usecolortheme{crane} 
  \usefonttheme{serif}  
  \setbeamertemplate{navigation symbols}{}
  \setbeamertemplate{caption}[numbered]
  \setbeamertemplate{theorems}[numbered]
  \setbeamertemplate{footline}
  {
    \leavevmode%
    \hbox{%
    \begin{beamercolorbox}[wd=.333333\paperwidth,ht=2.25ex,dp=1ex,center]{author in head/foot}%
      \usebeamerfont{author in head/foot}\insertshortauthor
    \end{beamercolorbox}%
    \begin{beamercolorbox}[wd=.333333\paperwidth,ht=2.25ex,dp=1ex,center]{title in head/foot}%
      \usebeamerfont{title in head/foot}\insertshorttitle
    \end{beamercolorbox}%
    \begin{beamercolorbox}[wd=.333333\paperwidth,ht=2.25ex,dp=1ex,right]{date in head/foot}%
      \usebeamerfont{date in head/foot}
      \insertframenumber{}% / \inserttotalframenumber
      \hspace*{2ex} 
    \end{beamercolorbox}}%
    \vskip0pt%
  }%
}
\makeatother
\renewcommand*{\thefootnote}{\fnsymbol{footnote}}
\usepackage[english]{babel}
\usepackage[utf8x]{inputenc}
\title[Musterthema kurz]{Musterthema zum Erforschen langer Musterstrukturen}
\author{Hans Mustermann\footnote{Text der Fußnote}}
\institute{Musteruniversität}

\AtBeginSection[]
{
  \begin{frame}<beamer>
    \frametitle{Outline}
    \tableofcontents[currentsection,currentsubsection]
  \end{frame}
}
\begin{document}
\begin{frame}
  \titlepage
\end{frame}
\end{document}