[NTG-context] Metafun example doesn't work

All, I've always wondered why this Metafun manual example doesn't work. \startMPgraphic draw unitsquare xscaled 5cm yscaled 1cm withpen pencircle scaled 2mm withcolor .625 red; \stopMPgraphic \hbox\bgroup \loadcurrentMPgraphic{width=5cm,height=1cm}\placeMPgraphic\quad \loadcurrentMPgraphic{width=8cm,height=1cm}\placeMPgraphic\egroup