Scrreprt indent after chapter heading after patchcmd

Question

In the following example, I've added a patch to the \chapter as an attempt to fix hyperref links. (See Hyperref chapter in twocolumn mode (without using multicols).)

\documentclass[parskip=half]{scrreprt}
\usepackage{hyperref}
\usepackage[twocolumn,landscape]{geometry}
\usepackage{etoolbox}
\makeatletter
\def\tmphook{\setlength{\HyperRaiseLinkLength}{\glueexpr\scr@chapter@sectionafterskip+35pt\relax}}
% \patchcmd{<cmd>}{<search>}{<replace>}{<success>}{<failure>}
\patchcmd{\chapter}{\@afterindentfalse}{\@afterindentfalse\leavevmode}{}{}
\patchcmd{\Hy@raisedlink}{\ifvmode}{\let\HyperRaiseLinkHook\tmphook\ifvmode}{}{}
\makeatother

\usepackage{lipsum}

\begin{document}
 \tableofcontents
 \chapter*{Preface}%
 \lipsum[1-5]
 \chapter{Introduction}
 \lipsum[1-5]
 \section{Lipsum}
 \lipsum[1-3]
\end{document}

This, however, gives me a weird indent only after non-starred \chapter headings. Some of the indent is removed by placing a % at the end, as \chapter{Introduction}%, but not all of it. For starred \chapter headings, the behaviour is similar, though I can remove the entire indent by using %.

The behaviour goes away when I comment out the line

\patchcmd{\chapter}{\@afterindentfalse}{\@afterindentfalse\leavevmode}{}{}

But this fails to solve the original problem. I've looked at the scrreprt.cls file to try to eyeball a bug, but don't have the expertise to identify it. The behaviour is only present in twocolumn format.

\newcommand\chapter{\if@openright\cleardoublepage\else\clearpage\fi
  \thispagestyle{\chapterpagestyle}%
  \global\@topnum\z@
  \@afterindentfalse
  \SecDef\@chapter\@schapter
}
\newcommand*{\@chapter}{}
\def\@chapter[#1]#2{%
  \ifnum \scr@osectarg=\z@
    \@scr@tempswafalse
  \else
    \scr@istest#1=\@nil
  \fi
  \if@scr@tempswa
    \setkeys{KOMAarg.section}{tocentry={#2},head={#2},#1}%
  \else
    \ifcase \scr@osectarg\relax
      \setkeys{KOMAarg.section}{tocentry={#1},head={#1}}%
    \or
      \setkeys{KOMAarg.section}{tocentry={#2},head={#1}}%
    \or
      \setkeys{KOMAarg.section}{tocentry={#1},head={#2}}%
    \or
      \setkeys{KOMAarg.section}{tocentry={#1},head={#1}}%
    \fi
  \fi
  \ifnumbered{chapter}{%
      \refstepcounter{chapter}%
      \@maybeautodot\thechapter
      \typeout{\@chapapp\space\thechapter.}%
      \ifx\scr@ds@tocentry\@empty\else
        \addchaptertocentry{\thechapter}{\scr@ds@tocentry}%
      \fi
  }{%
    \ifx\scr@ds@tocentry\@empty\else
      \addchaptertocentry{}{\scr@ds@tocentry}%
    \fi
  }%
  \expandafter\chaptermark\expandafter{\scr@ds@head}%
  \ifdim \@chapterlistsgap>\z@
    \doforeachtocfile{%
      \iftocfeature{\@currext}{chapteratlist}{%
        \addtocontents{\@currext}{\protect\addvspace{\@chapterlistsgap}}%
      }{}%
    }%
    \@ifundefined{float@addtolists}{}{%
      \scr@float@addtolists@warning
      \float@addtolists{\protect\addvspace{\@chapterlistsgap}}%
    }%
  \fi
  \if@twocolumn
    \if@at@twocolumn
      \@makechapterhead{#2}%
    \else
      \@topnewpage[\@makechapterhead{#2}]%
    \fi
  \else
    \@makechapterhead{#2}%
    \@afterheading
  \fi
}
\newcommand*{\@makechapterhead}[1]{%
  \use@chapter@o@preamble
  \@@makechapterhead{#1}%
  \use@preamble{chapter@u}%
}
\newcommand*{\@@makechapterhead}[1]{%
  \@tempskipa=\glueexpr \scr@chapter@sectionbeforeskip\relax
  \ifdim\@tempskipa<\z@\@tempskipa-\@tempskipa\fi
  \chapterheadstartvskip
  {%
    \setlength{\parindent}{\z@}\setlength{\parfillskip}{\fill}%
    \normalfont\sectfont\nobreak\nobreak\usekomafont{chapter}{}%
     \def\IfUseNumber{\ifnumbered{chapter}}%
    \if@chapterprefix
      \raggedchapter
      \let\IfUsePrefixLine\@firstoftwo
      \let\@tempa\@firstofone
    \else
      \let\IfUsePrefixLine\@secondoftwo
      \let\@tempa\@hangfrom
    \fi
    \@tempa{%
      \IfUseNumber{%
        \usekomafont{chapter}{%
          \IfUsePrefixLine{%
            {\usekomafont{chapterprefix}{%
                \chapterformat\chapterheadmidvskip
            }}%
          }{%
            \chapterformat
          }%
        }%
      }{}%
    }%
    {%
      \IfUsePrefixLine{}{\raggedchapter}%
      \interlinepenalty \@M
      \usekomafont{chapter}{#1}\par
    }%
  }%
  \nobreak\par\nobreak
  \@tempskipa=\glueexpr \scr@chapter@sectionafterskip\relax
  \ifdim\@tempskipa<\z@\@tempskipa-\@tempskipa\fi
  \chapterheadendvskip
}

Answer 1

For me the combination of your code and the part of the cited question from Werner seems to work for me. The copied part starts with % copy from http://tex.stackexchange.com/questions/230577, Werner and ends at \begin{document}.

Please check the following MWE:

\documentclass[parskip=half]{scrreprt}

\usepackage[twocolumn,landscape]{geometry}
\usepackage{lipsum}
\usepackage{hyperref}

\usepackage{etoolbox}
%\makeatletter
%\def\tmphook{\setlength{\HyperRaiseLinkLength}{\glueexpr\scr@chapter@sectionafterskip+35pt\relax}}
%% \patchcmd{<cmd>}{<search>}{<replace>}{<success>}{<failure>}
%\patchcmd{\chapter}{\@afterindentfalse}{\@afterindentfalse\leavevmode}{}{}
%\patchcmd{\Hy@raisedlink}{\ifvmode}{\let\HyperRaiseLinkHook\tmphook\ifvmode}{}{}
%\makeatother


% copy from http://tex.stackexchange.com/questions/230577, Werner    
% Add extra hyper target for chapter: chapter..\thechapter
\renewcommand*{\chapterformat}{%
  \mbox{\raisebox{25pt}[0pt][0pt]{\hypertarget{chapter..\thechapter}{}}% Add 
    \chapappifchapterprefix{\nobreakspace}\thechapter\autodot\enskip}%
}
\makeatletter
% Update \addcontentsline to jump to new hyper target _only_ if \chapter is used
\patchcmd{\addcontentsline}% <cmd>
  {\Hy@writebookmark}% <search>
  {\ifnum\pdfstrcmp{chapter}{#2}=0 % Chapter mark
     \edef\@currentHref{chapter..\thechapter}%
   \fi
   \Hy@writebookmark}% <replace>
  {}{}% <success><failure>
\makeatother


\begin{document}
 \tableofcontents
 \chapter*{Preface}%
 \lipsum[1-5]
 \chapter{Introduction}
 \lipsum[1-5]
 \section{Lipsum}
 \lipsum[1-3]
\end{document}

The result for the preface: