[NTG-context] nested tabulate

I get funny horizontal lines in this example \starttext \starttabulate[|p|p|] \HL \NC {\starttabulate[|c|c|] \HL \NC c\NC c\NC\NR \HL \NC c\NC c\NC\NR \stoptabulate} \NC Text \NC\NR\HL \NC C\NC C\NC\NR \HL \stoptabulate \stoptext minimal, mkii and mkiv Herbert