Scene doesn't nest

[Masterchef365]

Describe the bug
I'm very aware that this is a niche use-case, and must admit that I don't have an immediate application for it, but: nesting Scene doesn't provide the desired effect.

To Reproduce
Steps to reproduce the behavior (tested on master 0db56dc):

use eframe::egui::{self, Rect};

fn main() -> eframe::Result {
    let mut scene_rect = Rect::ZERO;
    let mut inner_rect = Rect::ZERO;

    eframe::run_simple_native("My egui App", Default::default(), move |ctx, _frame| {

        egui::CentralPanel::default().show(ctx, |ui| {
            ui.label("Outside the scenes");

            egui::Scene::new().show(ui, &mut scene_rect, |ui| {
                ui.label("Inside first scene");

                egui::Frame::canvas(ui.style()).show(ui, |ui| {
                    egui::Scene::new().show(ui, &mut inner_rect, |ui| {
                        ui.label("I'm in a nested scene!");
                    });
                });

            });
        });
    })
}

Expected behavior
Ideally, the contents of the sub-scene should be be scaled, transformed, and clipped appropriately.

Screenshots

Additional context
Again, I don't have an immediate use-case for this so it probably shouldn't be a priority.