Unstable formatting of GraphQL comments at end of argument list

Prettier 2.0.5
Playground link

--parser graphql

Input:

# Input1: the original input

query Browse(
  $offset: Int
  $limit: Int
  $categories: [String!]
  $search: String
  # $foo: Int
  # $bar: Int
) {
  t
}

# prettier(Input1): this is the result of formatting Input1, but 
# note the output differs. Formatting should be stable.

query Browse(
  $offset: Int
  $limit: Int
  $categories: [String!]
  $search: String
) # $foo: Int
# $bar: Int
{
  t
}

# prettier(prettier(Input1)): this is the result of formatting the
# formatted output of Input1. This *should* be the same as 
# `prettier(Input1)` but isn't.

query Browse(
  $offset: Int
  $limit: Int
  $categories: [String!]
  $search: String # $foo: Int
) # $bar: Int
{
  t
}

Output:

# Input1: the original input

query Browse(
  $offset: Int
  $limit: Int
  $categories: [String!]
  $search: String
) # $foo: Int
# $bar: Int
{
  t
}

# prettier(Input1): this is the result of formatting Input1, but
# note the output differs. Formatting should be stable.

query Browse(
  $offset: Int
  $limit: Int
  $categories: [String!]
  $search: String # $foo: Int
) # $bar: Int
{
  t
}

# prettier(prettier(Input1)): this is the result of formatting the
# formatted output of Input1. This *should* be the same as
# `prettier(Input1)` but isn't.

query Browse(
  $offset: Int
  $limit: Int
  $categories: [String!]
  $search: String # $foo: Int # $bar: Int
) {
  t
}

Expected behavior:

prettier(prettier(graphql)) should be the same as prettier(graphql); formatting should be stable.

Use the linked GraphQL Playground reproduction with the graphql parser as the starting point. Format the provided input twice and compare both outputs; done means prettier(prettier(graphql)) matches prettier(graphql), with the comment placement stable.