Hello all,

In the example below, I mean for a gray box with rounded corners to be placed behind \startC ... \stopC blocks. This example compiles properly on Linux with the latest ConTeXt beta and LuaTeX synced from the minimals just minutes ago.

On Windows, also updated from minimals this morning, I get the following error and no text background:

mplib           : initializing instance 'metafun' using format 'metafun'
mplib           : loading 'metafun.mp' from 'C:/context/tex/texmf-cache/luatex-c
ache/context/2fea56f92e5267d7cc9662e4d5f52e1e/formats/cont-en-metafun.mem'
! Emergency stop.
<inserted text> ...ore.mp ; fi ; ;;;]===], false)}

\processMPgraphic ...s ;\!!es , \MPaskedfigure )}}
                                                  \egroup \global \MPinstanc...
\useMPpositiongraphic ...tartMPcode #3\stopMPcode
                                                  \egroup
\doMPpositiongraphic ...riables \getvalue {MPG:#1}
                                                  }
\doMPpositiongraphic ...fined {MPG:#1}\donothing }
                                                  \removelastspace }\smashbo...
\dohandleMPpositiongraphicrange ...raphic {#3}{#4}
                                                  \fi \fi
...
l.59 \stoptext

!  ==> Fatal error occurred, no output PDF file produced!MTXrun | fatal error, r
eturn code: 1

Here is the example:

%%%%%
\unprotect

\startuseMPgraphic{mpos:par:myexample}
path p;
for i = 1 upto nofmultipars :
p := multipars[1] topenlarged 4pt bottomenlarged 4pt cornered 2mm ;
fill p withcolor 0.9white ;
draw p withcolor black
withpen pencircle scaled \MPvar{linewidth};
endfor;
\stopuseMPgraphic

\definetextbackground [listingbackground]
  [state=start,
   mp=mpos:par:myexample,
   location=paragraph,
   leftoffset=0em,
   rulethickness=1pt]

\definetyping [C]
  [option=commands]
\setuptyping [C]
  [bodyfont=8pt,
   margin=1em,
   before=%
     {\blank[big]
      \setupinterlinespace[line=1.6ex]
      \starttextbackground[listingbackground]},
   after=%
     {\stoptextbackground
      \blank[big]}]

\protect

\starttext

\input tufte

\starttyping
namespace Example
{
    int a;
    int b;
}
\stoptyping

\input knuth


\startC
namespace Example
{
    int a;
    int b;
}
\stopC

\stoptext
%%%%%