\addvspace after sections doesn't work properly

[u-fischer]

Without titlesec the \addvspace is work as expected and adds only minimal additional space:

\documentclass{article}
%\RequirePackage{titlesec}

\begin{document}
\tableofcontents

\section{a}
text
\section{b}\showthe\lastskip
\addvspace{1em}
text
\end{document}

> 9.90276pt plus 0.86108pt.
l.106 \section{b}\showthe\lastskip

If one uncomment titlesec \lastskip is zero and so the full addvspace is added. This also affects the tableofcontents which has now inconsistent spacing compared to normal sections:

> 0.0pt.
l.106 \section{b}\showthe\lastskip

[jbezos]

See https://tex.stackexchange.com/questions/37258/addvspace-after-a-titlesec-heading) . I’ll study it, for more use cases and a possible option to change the behavior.