Citations: Sort and Compress with superscript (Nature style) using non-superscript dash (xetex+Linux Libertine)

Question

Possible Duplicate:
How to change parameters for \textsuperscript{} in french?

solution: How to change parameters for \textsuperscript{} in french?

I passed the no-sscript option to xltxtra.

\usepackage[no-sscript]{xltxtra}

I'm using this to set up my citations/bibliography:

\usepackage[sectionbib,super,sort&compress]{natbib}
\usepackage{chapterbib}
\bibliographystyle{plain}

and it is working, sort-of, when I cite a range of sources in the output I get a the correct numbers (superscript) but the dash (when the range is compressed) is non-superscript.

Am I doing something wrong? Is there a way to tell it to use a proper super script dash so it doesn't look like 1_3.

Well, in making my MWE, it appears the issue is related to xetex+Linux Libertine font. If I use latex and the default font or Times New Roman the problem goes away, ie. I get the superscript dash. Any one know how to fix this without changing fonts? Thanks!

%!TEX TS-program = xelatex
%!TEX encoding = UTF-8 Unicode

% The bib file
\begin{filecontents*}{bib.bib}
@article{Bennett2011,
   author = {Bennett, S.},
   title = {Nitride semiconductors studied by atom probe tomography and correlative techniques},
   year = {2011}
}

@article{Bunton2010,
   author = {Bunton, J. and Olson, J. and Lenz, D. and Larson, DJ and Kelly, TF},
   title = {Optimized Laser Thermal Pulsing of Atom Probe Tomography: LEAP 4000X™},
   journal = {Microscopy and Microanalysis},
   volume = {16},
   number = {S2},
   pages = {10-11},
   year = {2010}
}

@article{Cherniak2000,
   author = {Cherniak, DJ},
   title = {Rare earth element diffusion in apatite},
   journal = {Geochimica et Cosmochimica Acta},
   volume = {64},
   number = {22},
   pages = {3871-3885},
   year = {2000}
}

@article{Clifford1959,
   author = {Clifford, A.F.},
   title = {The electronegativity of groups},
   journal = {The Journal of Physical Chemistry},
   volume = {63},
   number = {8},
   pages = {1227-1231},
   year = {1959}
}
\end{filecontents*}

% DOCUMENT LAYOUT
\documentclass[10pt, letterpaper]{article} 

%citations and bibliography
\usepackage[super,sort&compress]{natbib}
\bibliographystyle{plain}

% FONTS
\usepackage{fontspec}
\usepackage{xunicode}
\usepackage{xltxtra}
\defaultfontfeatures{Mapping=tex-text}
\setromanfont [Ligatures={Common}, Numbers={OldStyle}, Variant=01]{Linux Libertine O}

\begin{document}
\cite{Bunton2010, Cherniak2000,Clifford1959}
\footnotesize\bibliography{bib}
\end{document}