Discriminator dropdown shown for all variants

I have a base schema Pet with a discriminant petType and some schemas Cat, Dog and Lizard that inherit from it. When I use the Pet schema in documentation, I get the dropdown for petType as expected with each of the different types, but when I use the Cat type I also get the same, despite petType: "Cat" being the only valid value for this.

These are the types I get (first Pet and then Cat):

For the second one, I'd expect something like this instead:

These are the files that I'm using for this test case:

openapi: 3.0.2
info:
  title: Test API
  version: playground
servers: []

paths:
  /pets:
    get:
      summary: "Get all pets"
      responses:
        200:
          description: ""
          content:
            application/json:
              schema:
                type: object
                properties:
                  items:
                    type: array
                    items:
                      $ref: "#/components/schemas/Pet"
  /cats:
    get:
      summary: "Get all cats"
      responses:
        200:
          description: ""
          content:
            application/json:
              schema:
                type: object
                properties:
                  items:
                    type: array
                    items:
                      $ref: "#/components/schemas/Cat"

components:
  schemas:
    Pet:
      type: object
      description: "Pet superclass"
      required:
        - petType
      properties:
        petType:
          type: string
          description: "Pet type"
      discriminator:
        propertyName: petType
    Cat:
      description: "Cat subclass"
      allOf:
        - $ref: "#/components/schemas/Pet"
        - type: object
          # all other properties specific to a `Cat`
          properties:
            name:
              description: "Name"
              type: string
    Dog:
      description: "Dog subclass"
      allOf:
        - $ref: "#/components/schemas/Pet"
        - type: object
          # all other properties specific to a `Dog`
          properties:
            bark:
              description: "Bark"
              type: string
    Lizard:
      description: "Lizard subclass"
      allOf:
        - $ref: "#/components/schemas/Pet"
        - type: object
          # all other properties specific to a `Lizard`
          properties:
            lovesRocks:
              description: "Loves rocks"
              type: boolean

Start by loading the supplied OpenAPI 3.0.2 Pet/Cat example and compare the discriminator dropdown rendered for Pet with the one rendered for Cat. Trace the documentation schema-rendering entry point that produces these controls; done means the Cat view presents only its valid discriminator value rather than the full Pet variant list.