Arrow is too long when \vec followed by subscript or superscript after using unicode-math package

Question

The code is below

\documentclass[12pt]{article}    
\usepackage{unicode-math}    
\setmathfont{XITS Math}    
\begin{document}    
\large    
$\vec{a}^{12345}$    
\end{document}

Then the arrow of \vec is too long and penetrate the superscript 12. I just want the the arrow of \vec is above a, not whole of a^{12345} And I use xelatex to run the code.

However, if I replace $\vec{a}^{12345}$ with $\vec{ab}^{12345}$, then it looks quite good. The arrow of \vec is just above ab, it do not stretch and penetrate 12.

Can anyone tell me how to fix the problem?

Answer 1

This is a bug in XeTeX's math accent handling, should be fixed in the coming TeX Live 2012.

Answer 2

It seems like single-character arguments to \vec are handled differently. In that sense, supplying a fake two-element argument solves your problem:

$\vec{a{}}^{12345}