Loading the Linux Libertine Initials font breaks the `emph` command, even if the font is not used:

```
\documentclass{scrartcl}                                                        

\usepackage{fontspec}                                                           
\usepackage{xunicode}                                                           
\setmainfont[Mapping=tex-text]{Linux Libertine O}                               
\newfontfamily\lettrinefont{Linux Libertine Initials O}                         

\begin{document}                                                             

This is a test with \emph{emphasis}.                                            

\end{document} 

```

gives

![emph bug](https://i.stack.imgur.com/7wBsR.png)

Is this known? How can it be prevented (other than redefining `emph` to use Linux Libertine Slanted)?