[NTG-context] 2DOWN imposition gives blank pages

[Sanjoy Mahajan]

I'm learning page rearrangements and cannot figure out why the following
small example doesn't work (it's similar to those in the cont-eni.pdf
manual, fig 3.22).  Here it produces a two-page, blank PDF file when I
run 'texexec --arrange p2'
[ConTeXt ver: 2006.08.08 21:51 fmt: 2006.8.8 int: english mes: english]

\setuppapersize[A5][A4]
\setuparranging[2DOWN,rotated]
\setuplayout[width=fit,margin=0pt]

\starttext

\input tufte
\input tufte

\stoptext