The pdf from the tex below looks wrong to me, screenshot attached. It’s always like this when the page number in the second \definelayout is 1 more than the page number in the first. For other pairs of numbers, it behaves like I expect: the short layout is only on those 2 pages.

I’m using the LMTX I updated a few days ago. ConTeXt online’s pdf is the same.

%======================================================
\showframe
\setuppapersize[A4][A3,landscape] \setuparranging[2SIDE]
\setuplayout[backspace=80mm, width=100mm, topspace=50mm, header=0mm, footer=0mm, height=200mm, margindistance=10mm, leftmargin=40mm]

\definelayout[short][backspace=80mm, width=100mm, topspace=50mm, header=0mm, footer=0mm, height=80mm, margindistance=10mm, leftmargin=40mm]

\starttext 
\definelayout[2][short]
\definelayout[3][short]
\dorecurse{10}{\input{knuth} }  
\stoptext 
%======================================================

Also, https://wiki.contextgarden.net/Command/definelayout says:
% different layout for first two pages
\definelayout[1][wide]
\definelayout[3][reset]
This does not work for me.

Cheers, Peter