Hans,

after enabling image scaling in \insertpages
(https://mailman.ntg.nl/pipermail/ntg-context/2016/086114.html), I’m
afraid that the default value and compatibility in imposition is broken.

The minimal sample is the following:

\setuppapersize [A5][A4,landscape]
\setuparranging [2UP]
\setuplayout
[backspace=0pt,
topspace=0pt,
width=middle,
height=middle,
location=middle,
header=0pt,
footer=0pt]
\setupinteraction[state=start]
\setupinteractionscreen[option={landscape, paper}]
\starttext
\insertpages[whichever-document.pdf][width=0pt]
\stoptext

Would it be possible to restore the width value to its previous default?