[XeTeX] Problems with spacing in math formulae

[Christian Pech]

Hello,

I already reported this problem a week ago, but maybe the message got lost. 
The following latex-file produces wrong spacing when compiled with xelatex, but proper spacing when compiled with lualatex.

\documentclass{article}
\usepackage{fontspec}
\setmainfont{CMU Serif}

\usepackage[math-style=upright,vargreek-shape=TeX]{unicode-math}
\setmathfont{Neo Euler}

\begin{document}
\[  \sum_{i=1}^n \ldots\]
\end{document}



The result with xelatex looks as follows:


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while the result with lualatex look as follows:

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The obvious workaround, namely to use lualatex, is not good for me. I am actively using the input-mapping feature of xetex for editing a cyrillic (serbian) book that is written in latinica.

Does anybody have an idea, what is going on, and how I can circumvent the problem in xelatex?

Many thanks,
Christian