# Problem with \underbrace and Libertinus Math

I just switched to Libertinus Math and now have a problem with an \underbrace! While using Latin Modern as math font I get the expected result:

\documentclass{article}
\usepackage{amsmath}
\usepackage{mathtools}
\usepackage[
math-style=ISO,
bold-style=ISO,
partial=upright,
nabla=upright
]{unicode-math}
\usepackage{libertine}
%\setmathfont{Libertinus Math}
\usepackage{microtype}
\begin{document}
FAT-16: $\underbrace{\text{16-Bit}}_{\mathclap{\text{Größe einer Adresse (für das Speichern der Dateien)}}}\text{-Dateisystem}$

\end{document}


After switching to Libertinus Math the \underbrace has a wrong size:

Any idea how to fix it?

(ed.) minimal example

\documentclass{article}
\usepackage{unicode-math}
\setmathfont{Libertinus Math}
\begin{document}
$\underbrace{z}_{a}$
$\underbrace{zz}_{a}$
$\underbrace{zzz}_{a}$
$\underbrace{zzzz}_{a}$
$\underbrace{zzzzz}_{a}$
$\underbrace{zzzzzz}_{a}$
$\underbrace{zzzzzzz}_{a}$
\end{document}
% Local Variables:
% TeX-engine: luatex
% End:


Surprisingly, xelatex exhibits different output which fails less often:

\documentclass{article}
\usepackage{unicode-math}
\setmathfont{Libertinus Math}
\begin{document}
$\underbrace{z}_{a}$
$\underbrace{zz}_{a}$
$\underbrace{zzz}_{a}$
$\underbrace{zzzz}_{a}$
$\underbrace{zzzzz}_{a}$
$\underbrace{zzzzzz}_{a}$
$\underbrace{zzzzzzz}_{a}$
\end{document}
% Local Variables:
% TeX-engine: xetex
% End:


Here is using with the Libertinus as in TeXLive 2018 current pretest, updated. Things are much better but still a bit strange for zzz. In images below, maybe I have one more lines, because I extended mwe in the meantime.

With xetex at left and luatex at right:

• I have added more minimal example. There is also a problem with xelatex.... (I thought at first only lualatex) – user4686 Mar 25 '18 at 12:17
• works okay for me with the newest version of the font (in texlive 2018). – Ulrike Fischer Mar 25 '18 at 12:21
• Works for me too (xelatex and lualatex) – Christoph90 Mar 25 '18 at 12:31
• @UlrikeFischer confirmed on my updated TeXLive 2018. Strange line spacing discrepancy between xetex and luatex output (luatex's one is less spread out) – user4686 Mar 25 '18 at 12:37
• thus as first pointed by @UlrikeFischer it looks as if you only need latest Libertinus update. The images at bottom were taken with compilation using updated TL2018 pretest. – user4686 Mar 25 '18 at 12:47

The issue seems non-existent with latest Libertinus Math release, as currently available in TeXLive 2018 (pretest, libertinus texlive package having rev number 47077).