Confucius and LaTeX+pgfplots

\documentclass{standalone}

\usepackage{pgfplots}

\newcommand{\getpgfkey}[1]{\pgfkeysvalueof{/pgfplots/#1}}
\newcommand{\xmin}[0]{\getpgfkey{xmin}}
\newcommand{\xmax}[0]{\getpgfkey{xmax}}
\newcommand{\ymin}[0]{\getpgfkey{ymin}}
\newcommand{\ymax}[0]{\getpgfkey{ymax}}

\usepgfplotslibrary{groupplots}
\pgfplotsset{
xscalingdown/.style={ %XXX SCALE DOWN
    x coord trafo/.code=\pgfmathparse{##1/(1e#1)},
    xlabel style={
        append after command={
            node [anchor=base west] at (\tikzlastnode.base east) {$\cdot{10^{#1}}$}
        }
    },
    every axis/.append code={%
        \pgfmathresult{\xmax/(1e#1)}\global\let\xmaxSCALED=\pgfmathresult
        \pgfmathresult{\xmin/(1e#1)}\global\let\xminSCALED=\pgfmathresult
%       \pgfmathresult{\ymax}\global\let\ymaxSCALED=\pgfmathresult
%       \pgfmathresult{\ymin}\global\let\yminSCALED=\pgfmathresult
    },
},
xscalingup/.style={ %XXX SCALE UP
    x coord trafo/.code=\pgfmathparse{##1*(1e#1)},
    xlabel style={
        append after command={
            node [anchor=base west] at (\tikzlastnode.base east) {$\cdot{10^{{-1}#1}}$}
        }
    },
    every axis/.append code={%
        \pgfmathresult{\xmax*(1e#1)}\global\let\xmaxSCALED=\pgfmathresult
        \pgfmathresult{\xmin*(1e#1)}\global\let\xminSCALED=\pgfmathresult
        %\pgfmathresult{\ymax}\global\let\ymaxSCALED=\pgfmathresult
        %\pgfmathresult{\ymin}\global\let\yminSCALED=\pgfmathresult
    },
},
yscalingdown/.style={ %YYY SCALE DOWN
    y coord trafo/.code=\pgfmathparse{##1/(1e#1)},
    ylabel style={
        append after command={
            node [rotate=90, anchor=base west] at (\tikzlastnode.base east) {$\cdot{10^{#1}}$}
        }
    },
    every axis/.append code={%
        \pgfmathparse{\ymax/(1e#1)}\global\let\ymaxSCALED=\pgfmathresult
        \pgfmathparse{\ymin/(1e#1)}\global\let\yminSCALED=\pgfmathresult
        %\pgfmathresult{\xmax}\global\let\xmaxSCALED=\pgfmathresult
        %\pgfmathresult{\xmin}\global\let\xminSCALED=\pgfmathresult
    },
},
yscalingup/.style={ %YYY SCALE UP
    y coord trafo/.code=\pgfmathparse{##1*(1e#1)},
    ylabel style={
        append after command={
            node [rotate=90, anchor=base west] at (\tikzlastnode.base east) {$\cdot{10^{{-1}#1}}$}
        }
    },
    every axis/.append code={%
        \pgfmathparse{\ymax*(1e#1)}\global\let\ymaxSCALED=\pgfmathresult
        \pgfmathparse{\ymin*(1e#1)}\global\let\yminSCALED=\pgfmathresult
        %\pgfmathresult{\xmax}\global\let\xmaxSCALED=\pgfmathresult
        %\pgfmathresult{\xmin}\global\let\xminSCALED=\pgfmathresult
    },
},
}

\begin{document}
\begin{tikzpicture}
\begin{groupplot}[
group style={
    horizontal sep=0.2cm,
    group size=2 by 1,
    ylabels at=edge left,
    yticklabels at=edge left,
},
ymin=-100, ymax=1300,
xlabel={The label for the x-axis},
ylabel={Some y-values},
xscalingdown=3,
yscalingdown=3,
]
\nextgroupplot
\addplot coordinates{(2000,1200) (3000,\yminSCALED)};
\filldraw[ultra thick, dashed, blue] (\xminSCALED,\yminSCALED) rectangle (\xmaxSCALED,\ymaxSCALED);
\nextgroupplot
\addplot+ coordinates{(2100,1000) (2800,1200)};
\filldraw[ultra thick, dashed, red] (axis cs:2100,1000) rectangle (axis cs:\xmaxSCALED,1000) node[below, fill=orange] {bla};
%%NOTABLE DIFFERENT OUTPUT when omitting 'axis cs'
\filldraw[ultra thick, dashed, red] (2100,1000) rectangle (axis cs:\xmaxSCALED,1000) node[below, fill=orange] {bla};
\end{groupplot}
\end{tikzpicture}
\end{document}