This here works for the first columnset, but not for the second one:

=================================
\usemodule[newcolumnsets]

\definecolumnset[One][n=2]

\setupcolumnsetlines[One][1][1][9]
\setupcolumnsetlines[One][1][2][9]
\setupcolumnsetlines[One][2][1][9]
\setupcolumnsetlines[One][2][2][9]

\definecolumnset[Two][n=2]
\setupcolumnsetlines[Two][1][1][9]
\setupcolumnsetlines[Two][1][2][9]
\setupcolumnsetlines[Two][2][1][9]
\setupcolumnsetlines[Two][2][2][9]

\starttext
   \startcolumnset[One]
      \input knuth

      \input knuth
\stopcolumnset

\startcolumnset[Two]
      \input knuth

  \input knuth
\stopcolumnset
\stoptext
===================================

Am Sa., 17. Aug. 2019 um 15:14 Uhr schrieb Denis Maier <maier.de@gmail.com>:

> Ok, have tried it now. No change ...
>
> Am Sa., 17. Aug. 2019 um 13:33 Uhr schrieb Denis Maier <maier.de@gmail.com
> >:
>
>> Also, what about \setupcolumnsetlines[Two][2][1][9]?
>>
>> Denis Maier <maier.de@gmail.com> schrieb am Sa., 17. Aug. 2019, 13:32:
>>
>>> If I am remembering correctly, the documentation has
>>> \setupcolumnsetlines before \starttext.
>>>
>>> Sytse Knypstra <sytse.knypstra@home.nl> schrieb am Sa., 17. Aug. 2019,
>>> 12:59:
>>>
>>>> In an effort to balance columns in a columnset layout, I found that in
>>>> the following minimal example this effect is not obtained.
>>>> After commenting out the first three lines after \starttext the result
>>>> is ok.
>>>> I am wondering what I overlooked this time.
>>>>
>>>> \definecolumnset[Two][n=2]
>>>> \starttext
>>>>    \startcolumnset[Two]
>>>>       \input knuth
>>>>    \stopcolumnset
>>>>    \page
>>>>    \setupcolumnsetlines[Two][1][1][9]
>>>>    \startcolumnset[Two]
>>>>       \input knuth
>>>>    \stopcolumnset
>>>> \stoptext
>>>>
>>>> Thank you for your suggestions,
>>>>
>>>> Sytse Knypstra
>>>>
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>>>