[NTG-context] bug?: interaction between columns and background

Hello, When I place a graphic in the bacground and switch columns on, the background gets shifted for some reason. I hope that the problem will be evident from this example (since it behaves in a pretty random way - sometimes it's OK and sometimes it's pretty much shifted to the left). (Using ConTeXt version 2006.08.30 9:28) \startuseMPgraphic{TitleGraphic} draw unitsquare xyscaled (\overlaywidth-5mm,\overlayheight-5mm); \stopuseMPgraphic \defineoverlay [TitleGraphic] [\useMPgraphic{TitleGraphic}] \setupbackgrounds[page][background={TitleGraphic,page}] \starttext \startcolumns[n=3] \dorecurse{3}{\input tufte $$a^2+b^2=c^2$$} \stopcolumns \stoptext Thank you, Mojca