I reported this some days ago, but it was a rather short report, which
might explain why nobody has reacted upon it yet. So this time I'll go into
greater detail:

The grid system in columnsets works very well until the moment you include
a multiline equation somewhere. This causes the entire rest of the page to
be out of alignment with the grid. Try running this code with MkIV:

    \setuplayout
    [grid=yes]

    \setupindenting[yes,medium]

    \definecolumnset[example][n=2]

    \setupformulas[indentnext=auto]

    \starttext

    \showgrid

    \startcolumnset[example]
    \input knuth
    \input knuth
    \input knuth
    \startformula
    \startmathalignment
    \NC x^2 + y^2 \NC = z^2\NR[+]
    \NC u^2 + v^2 \NC = w^2\NR[+]
    \stopmathalignment
    \stopformula
    \input knuth
    \input knuth
    \input knuth
    \stopcolumnset

    \stoptext

A picture of the result can be found in this question on TeX.SE
<http://tex.stackexchange.com/questions/254815/grid-on-aligned-equations-in-context?noredirect=1#comment613211_254815>
.