metafun: Why is the arrow tip not filled?

Question

Trying out another example I saw that with the metafun format (luatex version) the arrow tips are no longer filled. The following document (to be compile with lualatex) shows the problem:

\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}

I have the problem on windows with TeXlive 2016, 2017 and miktex. In TeXlive 2015 it worked correctly. If I copy the metafun files from texlive\2017\texmf-dist\metapost\context to texlive 2015 it fails there too.

Can someone reproduce the problem and has an idea what could be the source?

Edit

I identified a problematic definition in mp-tool.mpiv (but I don't know yet why the fillup doesn't work, in context there seem to be no problem):

\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}

\begin{mplibcode}
def mfun_draw_arrow_path text t =
    if autoarrows :
        set_ahlength(t) ;
    fi
    draw arrowpath mfun_arrow_path t ;
    fill arrowhead mfun_arrow_path t ; %changed fillup to fill
    endgroup ;
enddef ;
beginfig(1);
drawarrow (0,0)--(10,10);
endfig;
\end{mplibcode}

\end{document}

Edit 2

Imho some important code is missing (my guess is that in context it is in mlib-pdf.lua) and so luamplib needs to be updated.

Edit 3

On the metapost mailing list, Hans Hagen confirm that new code is needed. He wrote

i have added some code to the luatex-mplib.lua module and it works in plain now so when i post a new context beta someone has to make sure it's also used in latex

and I added an issue to https://github.com/lualatex/luamplib/issues/71