Confusing with chunkBy

[Maksim via Digitalmars-d-learn]

Hello.
Why
chunkBy!((a,b) => a[1] == b[1])(
[
  [1,1],
  [1,2],
  [2,2],
  [2,1]
]);
returns a range with 3 subranges:
[
  [[1,1]],
  [[1,2], [2,2]],
  [[2,1]]
]
I thought it would returns a range with 2 subranges
[
  [[1,1], [2,1]],
  [[1,2],[2,2]]
]
It turns out that [1,1] and [2,1] are not grouped.

Thanks.