[XeTeX] unicode-math breakage with newest TL '10 update

[Joel C. Salomon]

(Technically this is OT for the XɘTeX list, but I suspect the folks who
can help me are here…)

Minimal test case:
	% !TEX TS-program = lualatex
	\documentclass{minimal}
	
	\usepackage{unicode-math}
	\setmathfont{Cambria Math}
	
	\begin{document}
	\[
		\dot x + \ddot y
	\]
	\end{document}
Works with XɘLaTeX, but LuaLatex gives me this error:

luaotfload | Font names database loaded:
/home/chesky/.texlive2010/texmf-var/luatex-cache/generic/names/otfl-names.lua(load:
/home/chesky/.texlive2010/texmf-var/luatex-cache/generic/fonts/otf/temp-cambria-cambria-math-1.lua)
! Missing control sequence inserted.
<inserted text>
                \inaccessible
l.5 \setmathfont{Cambria Math}

? h
Please don't say `\def cs{...}', say `\def\cs{...}'.
I've inserted an inaccessible control sequence so that your
definition will be completed without mixing me up too badly.
You can recover graciously from this error, if you're
careful; see exercise 27.2 in The TeXbook.
?

Any clues?

—Joel