openapi Union does not properly use flatten in documentation

[rsfunc]

Expected Behavior

For redoc for flatten endpoint I expect some help about the fields:

"other": "flatten",
"type": "ValueB",
"value": true
}

NOTE: the actual output of the endpoint is correct, only the documentation is not!

Actual Behavior

Steps to Reproduce the Problem

1. Compile the given sample

Cargo.toml

[package]
name = "example-openapi-flatten"
version.workspace = true
edition.workspace = true
publish.workspace = true

[dependencies]
poem = { version="3.1.6" }
poem-openapi = { version="5.1.5", features= ["redoc", "swagger-ui"]}
tokio = { version = "1.42.0", features = ["macros", "rt-multi-thread"] }
tracing-subscriber = {version = "0.3.19" }

Main.rs

use poem::{listener::TcpListener, Route, Server};
use poem_openapi::{
    param::Query,
    payload::{Json, PlainText},
    Object, OpenApi, OpenApiService, Union,
};

struct Api;

#[derive(Object)]
struct ValueA {
    pub value: bool,
}

#[derive(Object)]
struct ValueB {
    pub value: bool,
}

#[derive(Union)]
#[oai(one_of = true, discriminator_name = "type")]
enum UnionEnum {
    ValueA(ValueA),
    ValueB(ValueB),
}

#[derive(Object)]
struct Flatten {
    #[oai(flatten)]
    inner: UnionEnum,
    other: String,
}

#[OpenApi]
impl Api {
    #[oai(path = "/flatten", method = "get")]
    async fn flatten(&self) -> Json<Flatten> {
        Json(Flatten {
            inner: UnionEnum::ValueB(ValueB { value: true }),
            other: "flatten".into(),
        })
    }
}

#[tokio::main]
async fn main() -> Result<(), std::io::Error> {
    if std::env::var_os("RUST_LOG").is_none() {
        std::env::set_var("RUST_LOG", "poem=debug");
    }
    tracing_subscriber::fmt::init();

    let api_service =
        OpenApiService::new(Api, "Hello World", "1.0").server("http://localhost:3000/api");
    let ui = api_service.redoc();

    Server::new(TcpListener::bind("0.0.0.0:3000"))
        .run(Route::new().nest("/api", api_service).nest("/", ui))
        .await
}

Specifications

• Version: cargo 1.83.0 (5ffbef321 2024-10-29)
• Platform: osx
• Subsystem: