Optional is not working in nested schema

[menocomp]

First time to use this library and I like it :)
However I have an issue with optional strings:

The inferred string type is not marked as optional when schema is nested:

const PhoneSchema = createSchema(
  {
    req: Type.number({ required: true }),
    opt: Type.string(), // => I am setting 'opt' as optional
  },
  { _id: false, versionKey: false },
);

const UserSchema = createSchema(
  {
    req: Type.string({ required: true }),
    opt: Type.string(), // => I am setting 'opt' as optional
    phones: Type.array({ required: true }).of(PhoneSchema),
  },
  { _id: false, versionKey: false },
);

export type UserProps = ExtractProps<typeof UserSchema>;

Hover over UserProps I see this:

type UserProps = {
    req: string;
    phones: {
        req: number;
        opt: string;// 'opt' is not optional!
    }[];
    opt?: string; // 'opt' here is optional which is correct
}

I can only fix this by using of function on the object not in the schema as follows:

const phoneDefinition = {
  req: Type.number({ required: true }),
  opt: Type.string(),
};

const PhoneSchema = createSchema(phoneDefinition, {
  _id: false,
  versionKey: false,
});

const UserSchema = createSchema(
  {
    req: Type.string({ required: true }),
    opt: Type.string(),
    phones: Type.array({ required: true }).of(phoneDefinition),
  },
  { _id: false, versionKey: false },
);

Now I see correct optional fields as follows:

type UserProps = {
    req: string;
    phones: {
        req: number;
        opt?: string; =>  this is correct now
    }[];
    opt?: string;
}

Am I using this library correctly?
Is this a bug?