How do I make the time label in the following image appear as "10:00" (i.e. 10 o'clock) rather than the unexpected and unwelcome "09:60"?

Here's the code that I am using:
\documentclass{beamer}
\usepackage{pgfplots}
\usepgfplotslibrary{dateplot}
\begin{document}
\frame{
\begin{tikzpicture}
\begin{axis}[
mark =none,
xmin=2009-08-18 08:30,
xmax=2009-08-18 10:29,
ymin=0,
ymax=189,
grid=both,
axis x line=bottom,
axis y line=left,
date coordinates in=x,
minor x tick num=5,
minor y tick num=4,
xtick={2009-08-18 09:00,2009-08-18 10:00},
ytick={0,50,100,150},
xticklabel= \hour:\minute,
]
\addplot [thick,blue]coordinates {
(2009-08-18 08:30, 000)
(2009-08-18 09:00, 060)
(2009-08-18 09:20, 060)
(2009-08-18 10:00, 100)
(2009-08-18 10:10, 060)
} node [below] {Train A};
\end{axis}
\end{tikzpicture}
}
\end{document}
Supplementary question:
In the image above, why don't the minor tick lines appear before "09:00" but only after?

xtickmin to2009-08-18 8:30the minor tick lines reappear, so this looks like a bug; Similarly, if you make thextickmax to2009-08-18 10:10it works again. Odd. – Alan Munn May 18 '11 at 23:34