[XeTeX] Possible XeLatex bug observed using beamer class

[Martin Collier]

Hello,

I've found an inconsistency in colour management when using the beamer class
if using xelatex compared to the output of other engines. I can work around
this easily in my own code using the ifxetex package but suspect that it may
manifest a bug in how xetex processes something in the pgfval package. Below
is the minimal code to exhibit the behaviour. I don't know enough about
beamer keys or xetex to probe more deeply into why this happens but maybe it
is evidence of a bug in, rather than a feature of, xetex.

Regards,
Martin Collier

% start of code
% Minimal code to manifest possible bug
% indecisive.tex - I'm not sure of my preferred colour scheme (and neither
is Tex)
%
\documentclass{beamer}

\setbeamertemplate{background canvas}[vertical
shading][bottom=white,top=green] %...now change your mind
\setbeamertemplate{background canvas}[vertical
shading][bottom=green,top=white] % Tex should change too?

\begin{document}
\begin{frame}{Beamer exposes XeLaTex bug?}
% for a truly minimal example, comment out the next two lines and then
remove all comments
Is this slide green on the bottom?\par
Yes for lualatex and pdflatex, no for xelatex.\footnote{XeTeX, Version
3.1415926-2.2-0.9997.4 (MiKTeX 2.9 64-bit)\\}
\end{frame}
\end{document}
% One of the lines in the above file is redundant but which one depends on
the engine used - can this be right?
% end of code