Spurious space problem

Question

I have a problem of spurious space, but I can't find its origin.

Here is my MWE:

\documentclass{beamer}

\begin{document}
\begin{frame}{Dimensions et boites}{Commandes de manipulation des boites}
\parbox[c][.3\textheight][t]{\columnwidth}{%
%   \mbox{}%
    \only<+>{%
        \begin{itemize}
        \item Exemple: 
        \end{itemize}
        \parbox[c][.15\textheight][c]{\columnwidth}{%
            \centering\fbox{exemple}\raisebox{0pt}{\fbox{exemple}}\fbox{exemple}%
            \vphantom{\raisebox{-1ex}{\fbox{exemple}}\raisebox{\totalheight}{\fbox{exemple}}}
        }%
    }%
    \only<+>{%
        \begin{itemize}
        \item Exemple: 
        \end{itemize}
        \parbox[c][.15\textheight][c]{\columnwidth}{%
            \centering\fbox{exemple}\raisebox{1ex}{\fbox{exemple}}\fbox{exemple}
            \vphantom{\raisebox{-1ex}{\fbox{exemple}}\raisebox{\totalheight}{\fbox{exemple}}}
        }%
    }%
    \only<+>{%
        \begin{itemize}
        \item Exemple: 
        \end{itemize}
        \parbox[c][.15\textheight][c]{\columnwidth}{%
            \centering\fbox{exemple}\raisebox{\totalheight}{\fbox{exemple}}\fbox{exemple}
            \vphantom{\raisebox{-1ex}{\fbox{exemple}}\raisebox{\totalheight}{\fbox{exemple}}}
        }%
    }%
    \only<+>{%
        \begin{itemize}
        \item Exemple: 
        \end{itemize}
        \parbox[c][.15\textheight][c]{\columnwidth}{%
            \centering\fbox{exemple}\raisebox{-1ex}{\fbox{exemple}}\fbox{exemple}
            \vphantom{\raisebox{-1ex}{\fbox{exemple}}\raisebox{\totalheight}{\fbox{exemple}}}
        }%
    }%
}
\end{frame}
\end{document}

The \vphantom construction is here to make no vertical shift between the 4 baselines.

The first slide of the frame is slightly left shifted in comparison to the next 3, as shown on the picture below, resulting a bad looking animation.

Answer 1

You have \fbox{exemple}% in the first case but just \fbox{exemple} in the other cases so the spacing is out by one space.