[XeTeX] clash between \footnote and package xltxtra in document class scrbook from KOMA-script

[David Rangel]

Hello,

I have received the following complaint from XeLaTeX-xdvipdfmx while  
processing a simple
test scrbook (KOMA-Script) document.
________________________________________
(tex source document:)
________________________________________
\documentclass{scrbook}

\usepackage{fontspec}% provides font selecting commands
\usepackage{xunicode}% provides unicode character macros
\usepackage{xltxtra} % provides some fixes/extras (Breaks Footnotes in  
KOMA)

\begin{document}

a test of footnotes\footnote{a test}.

\end{document}
_________________________________________
(XeLaTeX error:)
_________________________________________

! Font \zf at basefont="" not loadable: installed font not found.
<to be read again>
                    \zf at family@fontdeflmr
l.16 a test of footnotes\footnote{
                                   a test}.
_________________________________________

The same document in the standard article document issues not error.   
There appears to be a
conflict between xltxtra and scrbook.  I looked at the old posting on  
the mailing list:
http://tug.org/mailman/htdig/xetex/2008-February/008731.html
but I am not sure if either this would be a workaround, or if I really  
even need xltxtra,
or if I should send this to the KOMA-script mailing list if it exists.  
Any ideas about how
xltxtra and the document class might be clashing?
Thank you,
David