Hi!

The document below compiled before, but not since upgrading to the new
version of standalone (current version: 2018.08.30 18:41). I'm running
linux if that matters.

The problem seem to be anglebetween, since if that line is commented out,
the file compiles.

%%%
\starttext
\startuseMPgraphic{testfig}
u:=1cm;
z0=origin;
z1=(4u,3u);
z2=(4u,0);

draw z0--z1--z2--cycle;

draw anglebetween(z0--z2,z0--z1,btex $\alpha$ etex);
\stopuseMPgraphic

\startplacefigure
\useMPgraphic{testfig}
\stopplacefigure
\stoptext
%%%

The error is something like:

tex error       > tex error on line 7 in file /home/mickep/tmp/testfil.tex:
! Extra }, or forgotten $

l.7 }

<local> \global \setbox \mptextbox \hbox {\clf_mptexttoks
                                                  }
<inserted text>
BAD
<to be read again>
\relax
\meta_process_graphic ...pvariableclass :}\relax }

\meta_process_graphic_stop...
\meta_handle_use_graphic ...a_process_graphic {#3}
                                                  \endgroup

/Mikael