perl6 syntax weirdness

json.pl6

> my $a = {a=>"A", b=>"B"}
{a => A, b => B}
> to-json $a
{
  "a": "A",
  "b": "B"
}
> to-json [$a]  # array of length 1
[
  {
    "a": "A",
    "b": "B"
  }
]
> to-json [{a=>"A", b=>"B"}] # array of length 2 - error
[
  {
    "a": "A"
  },
  {
    "b": "B"
  }
]
>