Comments between hash entries cause parse error

[Kelvin_L]

This should be self-explanatory:
On logstash 2.3.2

filter {
  mutate {
    rename => {
      # comment OK here
      "field_1a" => "field_1b"
      # comment not OK here - causes parse error
      "field_2a" => "field_2b"
      # comment OK here
    }
  }
}