Subfigure package misplaces last subfigure in full width environment

I am using subfigure package along with pdflatex. My paper is in two columns, and sometimes I use a full width figure with subfigures:

\begin{figure*}
\subfigure[AM06]{\includegraphics[width=.25\textwidth]{AR06_RUN03_vort.png}}
\subfigure[AM07]{\includegraphics[width=.25\textwidth]{AR07_RUN03_vort.png}}
\subfigure[AM08]{\includegraphics[width=.25\textwidth]{AR08_run03_vort.png}}
\subfigure[AM09]{\includegraphics[width=.25\textwidth]{AR09_run03_vort.png}}
\subfigure[AM10]{\includegraphics[width=.25\textwidth]{AR10_run03_vort.png}}
\subfigure[AM11]{\includegraphics[width=.25\textwidth]{AR11_run03_vort.png}}
\subfigure[AM12]{\includegraphics[width=.25\textwidth]{AR12_run03_vort.png}}
\subfigure[AM13]{\includegraphics[width=.25\textwidth]{AR13_run03_vort.png}}
\end{figure*}

As you can see from the image, it places the last subfigure in the wrong position. Any ideas on how I can debug this?