pgfplots - beamer reveals not working with "set layers"

Question

I am creating a pgfplot in beamer where visual elements are revealed step-by-step. In particular, I have added extra tick marks which appear in a later frame, using the visible on style described here.

I also have TikZ shapes which intersect with the axis, and I would like these to be displayed underneath the axis. I have tried using the set layers option of pgfplots, but this seems to ruin the reveal of the aforementioned tick marks - they just appear on the first frame, rather than a later frame. How can I ensure that both:

• the extra tick marks don't appear on the first frame; and
• shapes drawn inside the axis environment are placed underneath the axis?

Here is a MWE:

\documentclass{beamer}
\usepackage{pgfplots}
\tikzset{
    invisible/.style={opacity=0},
    visible on/.style={alt={#1{}{invisible}}},
    alt/.code args={<#1>#2#3}{%
        \alt<#1>{\pgfkeysalso{#2}}{\pgfkeysalso{#3}} % \pgfkeysalso doesn't change the path
    },
}
\begin{document}
\begin{frame}
\begin{center}
\begin{tikzpicture}
\begin{axis}[
    clip=false,xtick={0,1},
    extra x ticks={0.5},extra x tick style={visible on=<2->,grid=none},
    extra x tick labels={to appear later},
    xmin=-0.05,xmax=1.05,ymin=0,
    axis line style=semithick,
%   set layers=axis on top   % Uncommenting this ruins the reveal
]
    \addplot[domain=0:1,samples=300,visible on=<2->,color=blue,line width=1pt]{0.3-0.1*x} node(endofplot)[anchor=west]{$f$};
    \draw[fill=blue!50!white,opacity=0.95] (axis cs:0.3,-0.05) rectangle (axis cs:0.6,0.1) {};
\end{axis}
\end{tikzpicture}
\end{center}
\end{frame}
\end{document}

Answer 1

I am not entirely sure, but I think this is what you need:

\documentclass{beamer}
\usepackage{pgfplots}
\pgfplotsset{compat=newest}
\tikzset{
    invisible/.style={opacity=0},
    visible on/.style={alt={#1{}{invisible}}},
    alt/.code args={<#1>#2#3}{%
        \alt<#1>{\pgfkeysalso{#2}}{\pgfkeysalso{#3}} % \pgfkeysalso doesn't change the path
    },
}
\begin{document}
\begin{frame}
\begin{tikzpicture}
\begin{axis}[
    % set layers=true,
    axis on top=true,
    clip=false,
    xtick={0,1},
    extra x ticks={0.5},
    extra x tick style={visible on=<2>},
    extra x tick labels={to appear later},
    xmin=-0.05,
    xmax=1.05,
    ymin=0,
    ymax=0.3,
    axis line style=semithick,
]
\only<1->{\draw[fill=blue!50!white,opacity=0.95] (axis cs:0.3,-0.05) rectangle (axis cs:0.6,0.1) {};}
\only<2->{\addplot[domain=0:1,samples=300,visible on=<2->,color=blue,line width=1pt]{0.3-0.1*x} node(endofplot)[anchor=west]{$f$};}
\end{axis}
\end{tikzpicture}
\end{frame}
\end{document}