# Why is this edge not straight when using subgraphs in layered layout?

The MWE below produces a simple graph. When I add the two upper nodes A1 and B1 to a subgraph the horizontal alignment is lost which is understandable, since the nodes in the subgraph are positioned independent of the others. What I don't understand is that the connection from B1 to B3 is not straight anymore. How can I fix this while keeping the subgraph?

Note: I need to use subgraphs in a much more complex example where I get the same Problem.

\documentclass[border=0.125cm]{standalone}
\usepackage{tikz}
\usetikzlibrary{graphdrawing}
\usetikzlibrary{graphs,quotes}
\usegdlibrary{trees,layered,force}
\begin{document}
\tikz \graph[layered layout] {
"A1";
"B1";
"B3";
"A2";
"A3";
"C";
"A2" -- "A3";
"A3" -- "C";
"B1" --[minimum layers=2] "B3";
"A1" -- "A2";
"B3" -- "C";
};
\tikz \graph[layered layout] {
//[layered layout]{
"A1";
"B1";
};
"B3";
"A2";
"A3";
"C";
"A2" -- "A3";
"A3" -- "C";
"B1" --[minimum layers=2] "B3";
"A1" -- "A2";
"B3" -- "C";
};
\end{document}

• Though the question is not new I'm still hoping for some help. The problem is simple enough that other users might run into it. The graphdrawing library is a great alternative to graphviz but this bug makes it unusable for me. – dukeeloo Feb 14 '16 at 15:14

A late workaround: set bend left=0 for this edge or all edges:

%! TEX program = lualatex
\RequirePackage{luatex85}
\documentclass[border=0.125cm]{standalone}
\usepackage{tikz}
\usetikzlibrary{graphdrawing}
\usetikzlibrary{graphs,quotes}
\usegdlibrary{trees,layered,force}
\begin{document}
\tikz \graph[layered layout] {
"A1";
"B1";
"B3";
"A2";
"A3";
"C";
"A2" -- "A3";
"A3" -- "C";
"B1" --[minimum layers=2] "B3";
"A1" -- "A2";
"B3" -- "C";
};
\tikz \graph[layered layout,edges={bend left=0}] {
//[layered layout]{
"A1";
"B1";
};
"B3";
"A2";
"A3";
"C";
"A2" -- "A3";
"A3" -- "C";
"B1" --[minimum layers=2, bend left=0] "B3";
"A1" -- "A2";
"B3" -- "C";
};
\end{document}

• Late but still relevant to me:) I accepted this answer since it solves the problem in the MWE. When I try it on my bigger graph it produces the error: "Dimension too large. <recently read> \pgf@xa". When I simplify the graph the error goes away at some point but I dont know how to isolate the probelem. – dukeeloo May 17 '18 at 16:46