I find the following strange in columns. In the second \startcolumns\stopcolumns one would expect that the short text fragment in the column to the right, is placed in the wide open space on the first page. But in contrast, it is set to the left on a next page. Quite unnecessary, because in the column to the right there is enough space.
This behaviour seems to be initiated by the neighbourhood of the bottom of the page.

\setupcolumns[rule=on]
\showframe
\starttext
\startcolumns
	short text
\column
	\input tufte
\stopcolumns
\hairline
\startcolumns
	\input tufte
\column
	short text
\stopcolumns
\stoptext