CommonMarkViewer creates empty space above it after each update when used in a `Grid` about egui_commonmark

[zeozeozeo]

Here's how the attached example looks:

gridbug2.mp4

[lampsitter]

Repo without CommonMarkViewer

use eframe::egui;

fn main() {
    let native_options = eframe::NativeOptions::default();
    eframe::run_native(
        "Commonmark bug",
        native_options,
        Box::new(|_cc| Box::new(App::default())),
    )
    .expect("failed to run app");
}

#[derive(Default)]
struct App {
    content: String,
}

impl eframe::App for App {
    fn update(&mut self, ctx: &egui::Context, _frame: &mut eframe::Frame) {
        egui::CentralPanel::default().show(ctx, |ui| {
            egui::Grid::new("my_grid")
                .num_columns(2)
                .striped(true)
                .show(ui, |ui| {
                    ui.label("row 1, col 1");
                    ui.label("row 1, col 2");
                    ui.end_row();
                    ui.label("row 2, col 1");

                    let layout =
                        egui::Layout::left_to_right(egui::Align::BOTTOM).with_main_wrap(true);
                    ui.allocate_ui_with_layout(egui::vec2(200.0, 0.0), layout, |ui| {
                        ui.label(&self.content);
                    });
                });
        });
        self.content += "a";
        ctx.request_repaint();
    }

with_main_wrap is guilty. My naive guess is that the layout grows downwards, but the grid tries to center it, so it allocates space on both sides which is what causes the growth. I have tried different Align options but it does not appear to change anything.

I don't know whether this is a case of using egui wrong or if it's a bug in Grid.