[NTG-context] Columns: rule=on not working?

[context at vivaldi.net]

Hello,

the following code doesn't produce vertical rule between columns:

----
\starttext
   \startsimplecolumns[n=2,rule=on]
     \input knuth
   \stopsimplecolumns

   \blank

   \startcolumns[rule=on]
     \input knuth
     \column
     \input knuth
   \stopcolumns
\stoptext
----

My fault? Bug?

Best regards,

Lukas
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