Microtype affects font selection commands in center/flushleft/flushright

[gsalzer]

Description

The microtype package affects font selection commands in center/flushleft/flushright environments. The issue occurs with pdfTeX, LuaTeX and XeTeX (no other engines tested).

See also the discussion on tex.stackexchange.com.

Minimal example demonstrating the issue

\documentclass{article}
\usepackage{microtype}
\begin{document}
\begin{center}% or flushleft or flushright
  \Huge\sffamily\bfseries
  {\large Preheader}\\
  Header\\
  {\large Postheader}
\end{center}
\end{document}

Output:

Expected output:

Version information

• microtype 2025/02/11 v3.2a
• pdfTeX, Version 3.141592653-2.6-1.40.27 (TeX Live 2025) (preloaded format=pdflatex 2025.4.28)
• LaTeX2e <2024-11-01> patch level 2
  L3 programming layer <2025-03-26>
• article 2024/06/29 v1.4n
• l3backend-pdftex.def 2025-03-14 L3

Temporary fix

The issue goes away when either loading microtype with the option nopatch=item or when preceding the font selection commands with \leavevmode (suggested by Ulrike Fischer on tex.stackexchange).