[NTG-context] missing MP shading

hi list, i have some problems with reusing a picture in mp. the shading is missing, if the picture is shifted to another position (see minimal example). any help welcome. [program versions: the latest, the greatest..] greetings, peter \setuppagenumber[state=stop] \setupcolors[state=start] \startuniqueMPgraphic{test} save p,q; picture p; path q; q:= unitsquare xyscaled (OverlayWidth,.5OverlayHeight); p:= image(linear_shade(q,6,red,green)); addto currentpicture also p; addto currentpicture also (p yshifted .5OverlayHeight); \stopuniqueMPgraphic \defineoverlay[test] [\uniqueMPgraphic{test}] \starttext \framed[width=10cm,height=10cm,background=test]{} \stoptext