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

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