On the last few metres of typesetting a book I encountered a very nasty issue which I luckily managed to isolate in a MWE. The problem is that blockquotes patched with relsize to have a slightly reduced text size (next smaller "tex size" is too small for book format imho) leads to a diminished linespread in the preceding paragraph - if there is no empty line in the code before \begin{quote}.
Following MWE has more pronounced values to show the effect. Note the difference in the empty line in the code and the changed outcome for paragraph 1 and 2. With relsize of .9 (as in the real case) it's hardly visible.
Does this mean that the patching affects the preceding paragraph somehow? Seems like a bug since it only affects linespread and not text size.
Occurred with Texlive/Xetex but Overleaf/Latex produces the same problem. The problem seems to relate to the relsize part since I get a similar result with setspace/setstretch.
Some feedback on what went wrong would be appreciated, since I am a uneasy that issues like this might also happen in other instances, where I might not have noticed them yet.
\documentclass[fontsize=11.5pt,twoside]{scrreprt}
\usepackage{blindtext}
\usepackage{etoolbox}
\usepackage{relsize}
\linespread{1.8} %for effect
\AtBeginEnvironment{quote}{\relscale{.3}} %smaller than real, also for effect
\begin{document}
\subsection{problem}
\blindtext
\begin{quote}
\blindtext
\end{quote}
\blindtext
\begin{quote}
\blindtext
\end{quote}
\blindtext
\end{document}
\small
to resize a math display affects the baseline stretch of the preceding paragraph – barbara beeton Jul 9 '18 at 14:18