Disappearing arrowhead

Question

I have a curved arrow which works fine if the radius is 0.7 or smaller. But if I increase the radius to 0.8 then the arrowhead vanishes. Changing the various parameters doesn't seem to help. I would like to understand what is happening and how I can use a larger radius.

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{arrows, decorations.markings}
\begin{document}

\begin{tikzpicture}

    % https://tex.stackexchange.com/a/169115/2737
    \tikzset{
    curveArrow/.style={
      thick,
      decoration={markings,mark=at position
       1 with {\arrow[scale=1.5,semithick]{open triangle 60[fill=white]}}},
      double distance=3.5pt, shorten >= 8pt,
      preaction = {decorate},
      postaction = {draw,line width=1.4pt, white,shorten >= 8.5pt}
      }
    }
    % changing radius from 0.7 to 0.8 makes the arrow head disappear
    \draw[curveArrow] (0,0) arc (90:270:0.7); 

\end{tikzpicture}

\end{document}

Radius = 0.7 Radius = 0.8

Answer 1

Tikz library arrows is deprecated. I find it a bit strange to use markings just to place something at the very end of a path - maybe that is just me. Here is an altenative version without the artefacts and problems from the original code. The idea is to draw a triangle arrow first, and then make the double line exact long enough to draw over part of the vertical arrow line.

\documentclass[tikz, border=1cm]{standalone}
\usetikzlibrary{arrows.meta}
\begin{document}
\begin{tikzpicture}[
  curveArrow/.style={
    draw=none,
    preaction={draw, thick, -{Triangle[open, length=8pt 1, width=10pt]}},
    postaction={draw, thick, double distance=3.5pt, shorten >=8pt}
  }]
\draw[curveArrow] (0,0) arc (90:270:0.8); 
\end{tikzpicture}
\end{document}