"TeX capacity exceeded" error when converting markdown to PDF using XeLaTeX with russian language

The problem seems to reduce to this minimal example:

\documentclass{book}
\usepackage{fontspec}
\usepackage{polyglossia}

\defaultfontfeatures{Scale=MatchLowercase}

\setmainfont{Linux Libertine O}
\setmainlanguage{russian}

\begin{document}
x
\end{document}

which aborts with

! TeX capacity exceeded, sorry [input stack size=5000].
<to be read again> 
                   {

If the Scale=MatchLowercase option is removed, the document compiles. If I save the LaTeX file from your test with

pandoc --latex-engine=xelatex --toc --chapters -V mainfont="Linux Libertine O" -V lang="russian" -f markdown -w latex -s test.md > test.tex

and then remove the option, running XeLaTeX on test.tex is successful.

This is quite probably a bug in the Russian module for Polyglossia.