showshyphens misses some of the hyphenation points

[pgundlach]

\documentclass{article}
\usepackage[ngerman]{babel}
\usepackage{showhyphens}

\setlength{\textwidth}{0.01cm}
\setlength{\parindent}{0ex}

\begin{document}
    a-a % hyphen, supressing other hyphenations in the word

    aa-a

    a-aa

    a"=a % hyphen, allowing other hyphenations in the word

    a"~a % hyphen which supresses hyphenation at this place

    a\-a % hyphenation possibility, supressing other hyphenations

    a"-a % hyphenation possibility, allowing other hyphenations

    a""a % hyphenation possibility which does not need a hyphen

    a"|a % ligature breaker with hyphenation possibility
\end{document}

[Tchiller]

Also:

% arara: lualatex: {synctex: yes}

\documentclass{article}
\usepackage[english]{babel}
\usepackage[shortcuts]{extdash}
\setlength{\textwidth}{0.1cm}
\setlength{\parindent}{0ex}
\usepackage{showhyphens}

\begin{document}
multi\-/disciplinary

multi\Hyphdash{}disciplinary
\end{document}