When I redefine the command \cleardoublepage to include the words "This page has been intentionally left blank", the titles of the chapters are misaligned.
\documentclass{book}
\usepackage[a4paper, top=14mm, bottom=10mm, inner=15mm, outer=13mm, bindingoffset=10mm, includefoot, includehead, headsep=14mm, footskip=14mm]{geometry}
\usepackage{titlesec}
\titleformat{\chapter}[hang]{\normalfont\huge\bfseries}{\chaptertitlename\ \thechapter.}{1em}{}
\newcommand*{\blankpage}{%
\vspace*{\fill}
\centering [This page is intentionally left blank]
\vspace{\fill}}
\makeatletter
\renewcommand*{\cleardoublepage}{\clearpage\if@twoside \ifodd\c@page\else
\blankpage
\thispagestyle{empty}
\newpage
\if@twocolumn\hbox{}\newpage\fi\fi\fi}
\makeatother
\makeatletter
\begin{document}
\chapter{First chapter title.}
\chapter{Misaligned chapter title illustrating the bug I'm experiencing.}
\end{document}
Best Answer
This combines Werner's comment with a modified version of Ian Thompson's answer.
Werner's suggestion
Werner's suggestion resolves the problem mentioned in the question but reveals a further problem:
Centring the following text is probably not what was intended here and is therefore problematic.
Ian Thompson's answer
Ian Thompson's solution solves this problem but creates a third:
This happens because
\centering
is only effective when the paragraph ends and the grouping prevents the paragraph ending so the code is never actually effective.Final code