Strange pgfplots behaviour using fillbetween

Question

I'm using the following code to draw a simple graph and colour in the area under it. The expected result would be a fully filled-in area under the curve. The actual result is that the colouring is being clipped diagonally:

\documentclass{standalone}
\usepackage{tikz}
\usepackage{pgfplots}
\usepgfplotslibrary{fillbetween}
\pgfplotsset{compat = newest}
\begin{document}
\begin{tikzpicture}
\begin{axis}[xmin = 0.0, xmax = 1.0, ymin = 0.0, ymax = 1.0, enlarge x limits = 0.25, enlarge y limits = 0.25, axis x line = middle, axis y line = middle, x label/.append style = {at = {(current axis.right of origin)}, anchor = south west}, y label/.append style = {at = {(current axis.above origin)}, anchor = north west}, legend/.append style = {font = \small}, xtick = {0.3, 0.6}, xticklabels = {$\varphi_{1}$, $\varphi_{2}$}, ymajorticks = false, yminorticks = false, xlabel = $\varphi$, ylabel = $r$, name = polar]
\path [name path = axis] (axis cs:0,0) -- (axis cs:1,0);
\addplot [name path = r, smooth, mark = *] coordinates {
    (0.3, 0.6)
    (0.4, 0.65)
    (0.6, 0.5)
};
\addplot [fill = orange] fill between [of = r and axis, soft clip = {domain=0.3:0.6}];
\draw [dashed] (0.3, 0.6) -- (0.3, 0.6 |- {rel axis cs:0, 0});
\draw [dashed] (0.6, 0.5) -- (0.6, 0.5 |- {rel axis cs:0, 0});
\end{axis}
\end{tikzpicture}
\end{document}

Please advise.

Answer 1

I have no real solution for you but only a workaround. It seems that with lualatex there is rounding error problem. If you decrease the lower bound of the soft clip a tiny bit, it seems to work.

\documentclass{standalone}
\usepackage{tikz}
\usepackage{pgfplots}
\usepgfplotslibrary{fillbetween}
\pgfplotsset{compat = newest}

\begin{document}
\begin{tikzpicture}
\begin{axis}[xmin = 0.0, xmax = 1.0, ymin = 0.0, ymax = 1.0, enlarge x limits = 0.25, enlarge y limits = 0.25, axis x line = middle, axis y line = middle, x label/.append style = {at = {(current axis.right of origin)}, anchor = south west}, y label/.append style = {at = {(current axis.above origin)}, anchor = north west}, legend/.append style = {font = \small}, xtick = {0.3, 0.6}, xticklabels = {$\varphi_{1}$, $\varphi_{2}$}, ymajorticks = false, yminorticks = false, xlabel = $\varphi$, ylabel = $r$, name = polar]
\path [name path = axis] (axis cs:0,0) -- (axis cs:1,0);
\addplot [name path = r, smooth, mark = *] coordinates {
    (0.3, 0.6)
    (0.4, 0.65)
    (0.6, 0.5)
};
\addplot [fill = orange] fill between [of = r and axis, soft clip =
{domain=0.299:0.6}];
\draw [dashed] (0.3, 0.6) -- (0.3, 0.6 |- {rel axis cs:0, 0});
\draw [dashed] (0.6, 0.5) -- (0.6, 0.5 |- {rel axis cs:0, 0});
\end{axis}
\end{tikzpicture}
\end{document}

I stress that this is at best a workaround.