Metafun doesn' fill arrow heads anymore

Happy New Year to all the MetaPost users!

I’ve just experienced a problem discovered by Ulrike Fisher in

https://tex.stackexchange.com/q/408215/25768?sem=2

when the Metafun format of MetaPost is in use in the most recent TeX Live distributions (2016-2017), the arrow heads are not filled at all, they remain empty.

Try the example (in the LuaLaTeX) given by Ulrike to see this behaviour:

\documentclass{article}
\usepackage{luamplib}
\begin{document}

\begin{mplibcode}

beginfig(1);
drawarrow (0,0)--(10,10);
endfig;

\end{mplibcode}

\mplibsetformat{metafun}
\begin{mplibcode}

beginfig(1);
drawarrow (0,0)--(10,10);
endfig;
\end{mplibcode}

\end{document}

The first arrow head is normally filled, the second is not. Is it a bug, or simply the new default way Metafun draws an arrowhead?



--
http://tug.org/metapost/