In \boxedcolumns text a framed test gets extra (unwanted) depth (first example). This does not happen in \simplecolumns (second example). See the ABCD-boxes in the minimal example.
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\starttext
\startboxedcolumns[n=3]
\framed{ABCD}\blank\input knuth
\stopboxedcolumns
\blank
\startsimplecolumns[n=3]
\framed{ABCD}\blank\input knuth
\stopsimplecolumns
\stoptext