# smashoperator produces black line with Linux Libertine O

When I use to set the main font to "Linux Libertine O", the smashoperator command (and also mathclap and friends) produce a black line above the smashed subscript (with ).

\documentclass{minimal}
\usepackage{mathtools}
\usepackage{fontspec}
\setmainfont{Linux Libertine O}

\begin{document}

$\smashoperator{\sum_{i \in \mathrm{longidentifier}}} f(i)$

\end{document}


The problem does not occur with other fonts like Times New Roman or Linux Biolinum O. Is there a workaround?

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I think the problem boils down to the following. But I can't say if the font or the binaries (xetex has the problem too) is at fault as I have no idea what \radical0 (use by mathtools) is supposed to do and why it is affected by a change of the operator font.

Imho the best would be to ask the authors of mathtools.

\documentclass{article}
\usepackage[no-math]{fontspec}
\setmainfont{Linux Libertine O}
\ExplSyntaxOn
\DeclareSymbolFont{operators}\g_fontspec_encoding_tl\g_fontspec_mathrm_tl\mddefault\updefault
\ExplSyntaxOff
\pagestyle{empty}
\begin{document}
$\radical0 a$
\end{document}

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I don't get the line with xelatex (but I only have TL 2011 on the system I'm using). – egreg Aug 9 '12 at 16:35
@egreg: It also depends on the font. With an older version I didn't get the line either. – Ulrike Fischer Aug 9 '12 at 16:52
\radical combines a delimiter (first argument) with a horizontal line to create a square-root-like symbol. Apparently, giving 0 (=no delimiter) as argument usually disables also the horizontal line, except with the Libertine font. I reported this behavior to the mathtools author as well as in the Libertine bug tracker – cebewee Aug 9 '12 at 20:36