epígrafe e titlesec + titletoc criam mau comportamento

Question

Eu uso titlesec e titletoc para criar meu próprio estilo de capítulo que contém um minitoc após o título do capítulo. E eu uso epígrafe quando quero ter uma antes do título do capítulo.

Atualmente estou escrevendo um capítulo que contém várias seções, então o minitoc deve continuar na próxima página. Isto leva a uma impressão errada da epígrafe e as últimas seções não são impressas no exemplo a seguir:

\documentclass[11pt]{book}
\usepackage[utf8]{inputenc}     
\usepackage[T1]{fontenc}        


\usepackage{titletoc}
\usepackage{titlesec}
    \newlength{\HeightBeforeChap}
    \setlength{\HeightBeforeChap}{0pt}

    % redefine chapter style
    \titleformat{\chapter}[hang]{\filright}{}{0pt} 
        {\vspace*{\HeightBeforeChap} \\! \Huge \bfseries\raggedleft}
        [\vspace*{4pc}%
            \startcontents
            {\raggedright\bfseries \large Mini ToC \endgraf}
            \titlerule
            \vspace{6pt}
            \printcontents{p}{1}{\setcounter{tocdepth}{3}}
            \vspace{6pt}
            \titlerule
        ]

\usepackage{epigraph}
        \renewcommand{\textflush}{flushepinormal}
        \setlength\epigraphwidth{.55\textwidth}
        \makeatletter
            \@ifundefined{HeightBeforeChap}
            {% \HeightBeforeChap not defined
                }
            {% \HeightBeforeChap defined
                \renewcommand{\dropchapter}[1]{\setlength{\HeightBeforeChap}{#1} }
            }%
        \makeatother


\begin{document}

    \dropchapter{11pt}
    \chapter{title 1}

    \epigraphhead[40]{
            \epigraph{\itshape Computer programming is an art, because it applies 
                accumulated knowledge to the world, because it requires skill and ingenuity, 
                and especially because it produces objects of beauty.
            }{Donald Knuth, \textit{"Computer Programming as an Art". Communications of the ACM, Volume 17, Issue 12, dl.acm.org., December 1974}}
        }
    \dropchapter{0cm}

    \section{section 1}
    \subsection{title}
    \subsubsection{title}
    \section{section 2}
    \section{section 3}
    \section{section 4}
        \subsection{title}
        \subsubsection{title}
    \section{section 5}
    \section{section 6}
    \section{section 7}
        \subsection{title}
        \subsubsection{title}
    \section{section 8}
        \subsection{title}
        \subsubsection{title}
    \section{section 9}
        \subsection{title}
        \subsubsection{title}
    \section{section 10}
    \section{section 11}
    \section{section 12}
    \section{section 13}
        \subsection{title}
        \subsubsection{title}
    \section{section 14}
        \subsection{title}
        \subsubsection{title}
    \section{section 15}
        \subsection{title}
        \subsubsection{title}
    \section{section 16}
    \section{section 17}
    \section{section 18}
    \section{section 19}
        \subsection{title}
        \subsubsection{title}
    \section{section 20}
        \subsection{title}
        \subsubsection{title}
    \section{section 21}
        \subsection{title}
        \subsubsection{title}
    \section{section}

    \chapter{title 2}
    \section{title}

\end{document}

Aqui estão os resultados que obtenho:

Graças à resposta deegrégia, acho que está relacionado ao encerramento da página necessária para imprimir a epígrafe, mas não tenho ideia de como resolver.

Obrigado pela ajuda.

Answer 1

Como não há um único comentário mesmo depois da recompensa que coloquei, encontro uma solução feia, esperando soluções melhores do SE.

O feio:

\documentclass[11pt]{book}
\usepackage[utf8]{inputenc}     
\usepackage[T1]{fontenc}        

\usepackage{titletoc}
\usepackage{titlesec}
    \newlength{\HeightBeforeChap}
    \setlength{\HeightBeforeChap}{0pt}
    \newcommand{\BeforeChapCmd}{}
    \newcommand{\BeforeChap}[1]{\gdef\BeforeChapCmd{#1}}

    % redefine chapter style
    \titleformat{\chapter}[hang]{\filright}{}{0pt} 
        {\BeforeChapCmd\leavevmode\vspace*{\HeightBeforeChap}\BeforeChap{}\\ \Huge \bfseries\raggedleft}
        [\vspace*{4pc}%
            \startcontents
            {\raggedright\bfseries \large Mini ToC \endgraf}
            \titlerule
            \vspace{6pt}
            \printcontents{p}{1}{\setcounter{tocdepth}{3}}
            \vspace{6pt}
            \titlerule
            \leavevmode
        ]

\usepackage{epigraph}
    \renewcommand{\epigraphhead}[2][]{\BeforeChap{#2}   

\begin{document}

%   \dropchapter{11pt}
    \epigraphhead[40]{
                 \epigraph{\itshape Computer programming is an art, because it applies 
                     accumulated knowledge to the world, because it requires skill and ingenuity, 
                     and especially because it produces objects of beauty.
                 }{Donald Knuth, \textit{"Computer Programming as an Art". Communications of the ACM, Volume 17, Issue 12, dl.acm.org., December 1974}}
             }
    \chapter{title 1}
%    \dropchapter{0cm}

     \section{section 1}
     \subsection{title}
     \subsubsection{title}
     \section{section 2}
     \section{section 3}
     \section{section 4}
         \subsection{title}
         \subsubsection{title}
     \section{section 5}
     \section{section 6}
     \section{section 7}
         \subsection{title}
         \subsubsection{title}
     \section{section 8}
         \subsection{title}
         \subsubsection{title}
     \section{section 9}
         \subsection{title}
         \subsubsection{title}
     \section{section 10}
     \section{section 11}
     \section{section 12}
     \section{section 13}
         \subsection{title}
         \subsubsection{title}
         blabla blabla blabla blabla blabla blabla blabla blabla blabla blabla.
     \section{section 14}
         \subsection{title}
         \subsubsection{title}
     \section{section 15}
         \subsection{title}
         \subsubsection{title}
     \section{section 16}
     \section{section 17}
     \section{section 18}
     \section{section 19}
         \subsection{title}
         \subsubsection{title}
     \section{section 20}
         \subsection{title}
         \subsubsection{title}
     \section{section 21}
         \subsection{title}
         \subsubsection{title}
     \section{section}

     \chapter{title 2}
     \section{title}

\end{document}