This is a variation of the same MWE of this other question:
\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{calc}
\usetikzlibrary{spy}
\usetikzlibrary{backgrounds}
\begin{document}
\begin{tikzpicture}
[spy using outlines={circle, magnification=7, size=3cm, connect spies}]
\draw[->, very thick] (0,0) -- (5,0);
\path (2,2) node[fill, rectangle, inner sep=2pt, minimum height=1cm] (n) {};
\begin{scope}[on background layer]
\draw[dotted] (n.south west) -- (n.south west |- 0,0);
\draw[dotted] (n.south east) -- (n.south east |- 0,0);
\end{scope}
\spy on ($(n.south east |- 0,0)!0.5!(n.south west |- 0,0)$)
in node at (3,-2);
\end{tikzpicture}
\end{document}
This is the output:
As you can see, the dotted lines are missing from the spy in node. It seems that the spy library ignores the background layer.
Is there a way to make the contents of the background layer appear in the spy in node?
