PGFplots - `addplot` and `foreach` won't compile

I am trying to use some of the TikZ and PGFMath tools (e.g. pgfmathdeclarefunction and foreach) to make plotting things easier. However, I can’t get the following code to compile. There seems to be a bad interaction between the addplot command and the foreach command. It compiles fine when either of those is commented out, but not when they are both present.

documentclass{beamer}
usepackage{pgfplots}
pgfmathdeclarefunction{f}{1}{%
    pgfmathparse{0.3+0.3*#1-1*#1^2+0.65*#1^3}%
}

begin{document}

begin{frame}
begin{center}
begin{tikzpicture}
begin{axis}
    addplot{{f(x)}} node(endofplot)[anchor=west]{$f$};
    foreach n in {8,12,16}
        node [above] at (n,0) {$n$};
end{axis}
end{tikzpicture}
end{center}
end{frame}

end{document}

documentclass{beamer}
usepackage{pgfplots}
pgfmathdeclarefunction{f}{1}{%
    pgfmathparse{0.3+0.3*#1-1*#1^2+0.65*#1^3}%
}

begin{document}

begin{frame}
begin{center}
begin{tikzpicture}
begin{axis}
    addplot{{f(x)}} node(endofplot)[anchor=west]{$f$};
    foreach n in {8,12,16}
        edeftemp{noexpand
           node [above] at (n,0) {$n$};
        }temp
end{axis}
end{tikzpicture}
end{center}
end{frame}

end{document}