In egui 0.21.0, but not before, bottom panel slowly grows if radio buttons try to expand it

[John-Nagle]

Describe the bug
Here we have a game-type interface, with a TopBottomPanel menu bar at the top and a TopBottomPanel band of widgets at the bottom.
The bottom panel has a translucent grey background. It's suppose to size itself to the content.

Sizing worked prior to egui 0.21.0, but in 0.21.0, something very strange happens. Note the column of radio buttons, "Walk/Run/Fly". That column is slightly higher than the other widgets in the bar. The bar expands upward, and keeps slowly expanding until it fills the whole screen. See picture.

Relevant egui code is:

        egui::Frame::none()
            .fill(PANEL_BACKGROUND_COLOR)
            .rounding(OUTLINE_BOX_ROUNDING)
            .show(ui, |ui| {
            ui.horizontal_top(|ui| {
                ui.vertical(|ui| {
                        // Walk/run/fly
                        ui.radio_value(&mut walk_mode, WalkMode::Walk, t!("menu.walk", dict));
                        ui.radio_value(&mut walk_mode, WalkMode::Run, t!("menu.run", dict));
                        ui.radio_value(&mut walk_mode, WalkMode::Fly, t!("menu.fly", dict));
                        }

The enclosing TopBottomPanel code:

           //  Bottom button panel
            egui::TopBottomPanel::bottom("bottom_panel")
                .frame(Frame::none().fill(TRANSLUCENT_GREY_COLOR32))
                .show(&ctx, |ui| {
                    ui.visuals_mut().widgets.inactive.bg_fill = egui::Color32::TRANSPARENT; // transparent button background
                    ui.with_layout(egui::Layout::bottom_up(egui::Align::LEFT), |ui| {
                        ui.horizontal(|ui| {
                            //  Basic camera controls -- orbit, zoom, move
                            ui.add_space(OUTLINE_BOX_ROUNDING); // allow extra space before next item ***TEMP***
                            self.panel_camera.draw(ui, state);
                            //  Movement controls - walk, run, fly, stand.
                            ui.add_space(OUTLINE_BOX_ROUNDING); // allow extra space before next item ***TEMP***
                            self.panel_movement.draw(ui, state);
                            //  Chat controls - input text box
                            ui.add_space(OUTLINE_BOX_ROUNDING); // allow extra space before next item ***TEMP***
                            self.panel_chat.draw(ui, state);
                        })                
                    });
                });

self.panel_movement.draw(ui, state) is drawing the 3 radio buttons. Everything else expands the bottom bar as needed, but it doesn't

All this is running on top of Rend3 and rend3-egui, on Ubuntu Linux 20.04 LTS. Standalone application, not in a browser.

To Reproduce
Don't have a standalone test case, sorry.

Expected behavior
The TopBottomPanel.bottom() should be expanded to include all the radio buttons.

Screenshots

Desktop (please complete the following information):

• OS: Ubuntu Linux
• Version 20.04 LTS

Additional context
I may not be doing the layout in the ideal way, but this behavior is so weird it should be reported.

[John-Nagle]

This seems to be related to using bottom_up. If I do everything top_down, it works right. So I will stick to top_down for now.