OpenApi Spring generator - missing model files

Question

I can sucessfully generate Spring API and model files using gradle, OpenApi generator plugin ("org.openapi.generator" version "4.2.1").

I have a single api.yml file:

openapi: 3.0.2
info:
  title: API Documentation
  version: 1.0.0
servers:
  - url: http://localhost:8080/
tags:
  - name: Users
paths:
  /users:
    post:
      requestBody:
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/Parent'
      responses:
        200:
          description: New user created

components:
  schemas:

    Parent:
      required:
        - status
      properties:
        status:
          type: string
      discriminator:
        propertyName: status
        mapping:
          CHILD_ONE: '#/components/schemas/ChildOne'
          CHILD_TWO: '#/components/schemas/ChildTwo'

    ChildOne:
      allOf:
        - $ref: '#/components/schemas/Parent'
        - type: object

    ChildTwo:
      allOf:
        - $ref: '#/components/schemas/Parent'
        - type: object

And code generation produces Java Spring interface file and 3 model files: Parent.java, ChildOne.java and ChildTwo.java - 2 children classes extend the Parent class as expected.

However, when I split api.yml into 2 files (see below), ChildOne.java and ChildTwo.java are completely missing (there is only Parent.java file generated):

api.yml file:

openapi: 3.0.2
info:
  title: API Documentation
  version: 1.0.0
servers:
  - url: http://localhost:8080/
paths:
  /users:
    $ref: './api-sub.yml#/test'

api-sub.yml file:

test:
   post:
      requestBody:
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/Parent'
      responses:
        200:
          description: New user created

components:
  schemas:
    Parent:

      required:
        - status
      properties:
        status:
          type: string
      discriminator:
        propertyName: status
        mapping:
          CHILD_ONE: '#/components/schemas/ChildOne'
          CHILD_TWO: '#/components/schemas/ChildTwo'

    ChildOne:
      allOf:
        - $ref: '#/components/schemas/Parent'
        - type: object

    ChildTwo:
      allOf:
        - $ref: '#/components/schemas/Parent'
        - type: object

Generation passes without errors but only 1 class - Parent.java is generated:

// [...]
// Imports etc....
// [...]

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.PROPERTY, property = "status", visible = true)
@JsonSubTypes({
  @JsonSubTypes.Type(value = ChildOne.class, name = "CHILD_ONE"),
  @JsonSubTypes.Type(value = ChildTwo.class, name = "CHILD_TWO"),
})

public class Parent   {
  @JsonProperty("status")
  private String status;

// [...]
// Getters, setters etc....
// [...]

Why 2 other classes ChildOne.java and ChildTwo.java are not generated?

Please note that generator is seeing them as it uses their names and mappings in Parent.java.

I did some investigations and I've noticed that when I move schema definitions from api-sub.yml into api.yml like this:

api.yml file:

openapi: 3.0.2
info:
  title: API Documentation
  version: 1.0.0
servers:
  - url: http://localhost:8080/
paths:
  /users:
    $ref: './api-sub.yml#/test'

components:
  schemas:

    Parent:
      required:
        - status
      properties:
        status:
          type: string
      discriminator:
        propertyName: status
        mapping:
          CHILD_ONE: '#/components/schemas/ChildOne'
          CHILD_TWO: '#/components/schemas/ChildTwo'

    ChildOne:
      allOf:
        - $ref: '#/components/schemas/Parent'
        - type: object

    ChildTwo:
      allOf:
        - $ref: '#/components/schemas/Parent'
        - type: object

api-sub.yml file:

test:
   post:
      requestBody:
        content:
          application/json:
            schema:
              $ref: 'api.yml#/components/schemas/Parent'
      responses:
        200:
          description: New user created

Then, 4 files are generated: Parent.java, ChildOne.java, ChildTwo.java and (surprise) Parent2.java.

Parent2.java is semantically the same as Parent.java, just different name.

Any idea why is it so? Is there are bug in OpenApi generator?

Edit:

Yet another observation:

When I use a child somewhere in any endpoint e.g. (just for testing) in response, then this particular child is generated (but not the other one):

test:
   post:
      requestBody:
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/Parent'
      responses:
        200:
          description: New user created
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/ChildOne'

### [...]
### rest of api-sub.yml with schemas
### [...]

Does the child entity needs to be used to be generated? I've noticed such a behavior somewhere else beside of inheritance case.