\setupnote[footnote][location=lastcolumn] % <- causes layout problem
\definecolumnset[two][n=2]
\enablemode[twocolumns] % columnsets|twocolumns
\starttext
\doifmode{twocolumns}{\startcolumns}
\doifmode{columnsets}{\startcolumnset[two]}
\dorecurse{2}{\input knuth}\footnote{\input tufte}
\dorecurse{2}{\input knuth}
\doifmode{twocolumns}{\stopcolumns}
\doifmode{columnsets}{\stopcolumnset}
\stoptext
Thank you in advance
Andreas