How to adjust line spacing in wrapped chapter lines with KOMA-script?

Question

I'm using scrbook. Some chapter titles are long and wrap, some of those even twice. When it goes on the third line, the spacing is different than that between the first and second lines. Looks terribly annoying (sorry for the lousy screenshot):

I've no idea why this happens, and I can't fix it.

There's substantial "literature" here on TeX.SE on formatting titles. The closest it gets to is the very nice discussion in Control line spacing of section headings, but it uses titlesec, so not an option. I tried to redefine \chapterformat, doesn't help:

\renewcommand*{\chapterformat}{\normalfont\large\bfseries}{%
\thechapter}{1em}{\setstretch{0.1}}

I tried to apply the two solutions in Changing the linespacing of headings independently from the rest of the text. The one with the \setstretch in the mandatory argument just scales what there is. The other doesn't have any effect. The best thing that worked is looseness=-1, but it breakes "syntactic" in two.

EDIT: All apologies, here's a MWE:

\documentclass[a4paper,10pt,headings=optiontohead,version=last,openany]{scrbook}
\usepackage{kantlipsum}\date{}
\usepackage{suffix}
\renewcommand{\sectionmark}[1]{}%prevent rewriting \markright 
\renewcommand{\subsectionmark}[1]{}%prevent rewriting \markright 
\newcommand{\chapterauthor}[1]{\authortoc{#1}\printchapterauthor{#1}\markright{#1}}% setting \markright to author

\makeatletter
\newcommand{\printchapterauthor}[1]{%
 {\parindent0pt\vspace*{-10pt}%
 \linespread{1.1}\large\scshape#1%
 \par\nobreak\vspace*{30pt}}
 \@afterheading%
}
\newcommand{\authortoc}[1]{%
 \addtocontents{toc}{\vskip-10pt}%
 \addtocontents{toc}{%
 \protect\contentsline{chapter}%
 {\hskip1.3em\mdseries\scshape\protect\scriptsize#1}{}{}}
 \addtocontents{toc}{\vskip5pt}%
}
\makeatother
%% chapter formatting 
%% based on https://tex.stackexchange.com/a/173857/12934
\makeatletter
\renewcommand{\@chapapp}{}% remove the word `chapter'
\renewcommand*{\chapterformat}{%
  \linespread{2.5}\chapappifchapterprefix{\ }\thechapter\autodot\enskip}

\def\@makechapterhead#1{%
\vspace*{10\p@}%
{\parindent \z@ \raggedleft \reset@font
    \Huge \sffamily \@chapapp{}  \thechapter\vspace*{-15\p@}
    \par\nobreak
    \interlinepenalty\@M\hrulefill\newline\vspace*{-5\p@}
    \LARGE \sffamily #1\par\nobreak
    \vspace*{-8\p@}%
    \hrulefill
    \par\nobreak
    \vskip 30\p@
}}

\def\@makeschapterhead#1{%
\vspace*{4\p@}%
{\parindent \z@ \raggedleft \reset@font
    \sffamily
    \interlinepenalty\@M\hrulefill\newline\vspace*{-5\p@}
    \Huge \bfseries #1\par\nobreak
    \vspace*{-8\p@}%
    \hrulefill
    \par\nobreak
    \vskip 30\p@
}}

\begin{document}
\chapter{The walzing wombat went to the lazy lizard to get to the
dixie dancing ducks to have a meal of beloved bananas}
\kant[2]
\end{document}

I think now that the custom formatting is triggering it somehow...

Answer 1

For a lack of the actual code, i cannot really tell why this spacing is introduced, but here a solution using KOMA-only methods.

\documentclass[english]{scrbook}
\usepackage[utf8]{inputenc}
\usepackage{babel}
\usepackage{blindtext}

\KOMAoption{chapterprefix}{true}
\renewcommand*\raggedchapter{\raggedleft}
\addtokomafont{chapter}{\large}
\renewcommand*{\chapterformat}{\thechapter\autodot\IfUsePrefixLine{}{\enskip}}
\RedeclareSectionCommand[beforeskip=0pt]{chapter}
\renewcommand{\chapterheadmidvskip}{%
    \par\nobreak\vskip -.1cm {\rule{.4\textwidth}{.5pt}}\par%
}
\renewcommand{\chapterheadendvskip}{%
    \begingroup
    \raggedchapter
    \rule{0.9\textwidth}{.5pt}\par%
\vspace*{\baselineskip}%
\endgroup
}

\usepackage{geometry}% Just for this test
\geometry{ margin=7cm }
\begin{document}
\blinddocument
\chapter{The walzing wombat went to the lazy lizard to get to the
dixie dancing ducks to have a meal of beloved bananas}
\blindtext
\end{document}

With a bit of tweaking, we get this:

\documentclass[english]{scrbook}
\usepackage[utf8]{inputenc}
\usepackage{babel}
\usepackage{blindtext}
\usepackage{libertine}

\KOMAoption{chapterprefix}{true}
\renewcommand*\raggedchapter{\raggedleft}
\setkomafont{chapter}{\normalfont\large\sffamily}
\renewcommand*{\chapterformat}{\thechapter\autodot\IfUsePrefixLine{}{\enskip}}
\RedeclareSectionCommand[beforeskip=0pt]{chapter}
\renewcommand{\chapterheadmidvskip}{%
    \par\nobreak\vspace{\baselineskip}{\rule[.7\baselineskip]{.4\textwidth}{.4pt}}\par%
}
\renewcommand{\chapterheadendvskip}{%
\begingroup%
\raggedchapter%
\rule{\textwidth}{.5pt}\par%
\vspace*{\baselineskip}%
\endgroup%
}

\usepackage{geometry}
\geometry{ margin=6.9cm }
\begin{document}
\blinddocument
\chapter{The walzing wombat went to the lazy lizard to get to the
dixie dancing ducks to get some of their beloved bananabread}
\blindtext
\end{document}