[NTG-context] help with confusion re chapter number

[jbf]

Hi, I wonder if someone could lead me out of my current confusion.

In a test example with MWE as follows, I get exactly what I want:

\setuplabeltext [en] [chapter=~]
\define[2]\MyChapter
   {\framed[frame=off,width=broad,align=middle]{#1\blank[1cm]#2}}
\setuphead [chapter] [command=\MyChapter]
\chapter{Chapter title}

which gives me a chapter number (without the word 'Chapter') and 1cm 
below it the chapter title, e.g.:

              1

   My chapter title

But when I transfer this to the actual tex file I am working with, I 
lose the chapter number. Admittedly, there is more complication to my 
setup in the 'real' example, and maybe that's where I've gone wrong, but 
why am I losing the chapter number?

\define[2]\MyChapter
{\framed[frame=off,width=broad,align=middle,number=yes]{#1\blank[1cm]#2}}
\setuphead
[chapter][header=empty,alternative=middle,style=bold,numbercommand=\groupedcommand{}{\blank[2cm]},after={\blank[3cm]},command=\MyChapter]

Julian