I'm having some difficulties with nested itemgroups. I've produced a
minimal working example as follows.

\defineitemgroup
  [test] [symbol=n]

\starttext

% \startitemgroup
%   \startitem
%     \startitemgroup[test]
%       \startitem
%         ...
%       \stopitem
%     \stopitemgroup
%   \stopitem
% \stopitemgroup

\startitemgroup
  \startitem
    \startitemgroup
      \startitem
        Lorem ipsum
        \startitemgroup[test]
          \startitem
            dolor sit amet,
          \stopitem
          \startitem
            consectetur adipisicing elit.
          \stopitem
        \stopitemgroup
      \stopitem
    \stopitemgroup
  \stopitem
\stopitemgroup

\stoptext

I would expect items in the [test] itemgroup to be numbered 1, 2 but
instead they are both 0. I have also found out that, bizarrely,
uncommenting the first itemgroup fixes the issue. This is the behaviour I
get on the TeXLive 2016 version of ConTeXt, I don't have the latest
minimals installed to test.

Thanks in advance for any help with this matter!