chunkBy limitation?

[Dmitri via Digitalmars-d-learn]

I wondered if this is a current limitation of chunkBy 
implementation:

// http://dpaste.dzfl.pl/52d6a0c5d0ab
void bar(int[] foo)
{
        bool less(int a, int b) // contrived
        {
                return a < b;
        };
        foo.sort!less.groupBy;
}

resulting in:

/opt/compilers/dmd2/include/std/algorithm/iteration.d(1529): 
Error: function f351.bar.SortedRange!(int[], 
less).SortedRange.groupBy!().groupBy.ChunkByImpl!(__lambda1, 
int[]).ChunkByImpl.Group.popFront cannot access frame of function 
f351.bar.SortedRange!(int[], less).SortedRange.groupBy!().groupBy
...

I can see that the implementation of chunkBy is nested:
struct ChunkByImpl
{
        static struct Group {}
}

and that the predicate (less in this case) is accessed from the 
nested struct Group which is, probably, what's causing the 
compilation error.

The question is if this is an implementation error (i.e. Group 
should probably be moved to the top level) or a compiler issue?

Thanks in advance.