GTK4: focus leaving last-focused-child in GtkNotebook and then back into it

main.c

// Compile with:
//     gcc $(pkg-config --cflags gtk4)  -o main ./main.c $(pkg-config --libs gtk4) && ./main
//
// Run with:
//     ./main
//
// Reproduce issue:
//
//     1. Click on Page 2
//     2. Select "view3" and type something.
//     3. Go back to Page1, focus should be inside "view1"
//     4. IMPORTANT: Now go back to Page 2
//
//     Expectation: "view3" is focused, because it was the last-focused element
//     Actual: "view2" is focused!
//
//     In console you can see that when switching to Page 2, focus leaves "view1", then goes into view3, but then out again!
//
//          notebook: switch-page
//          view1 focus: leave
//          box1 focus: leave
//          box2 focus: enter
//          paned focus: enter
//          view3 focus: enter
//          view3 focus: leave <-- WHY?
//          paned focus: leave <-- WHY?
//          box2 focus: leave <-- WHY?
//          box2 focus: enter <-- WHY?
//          paned focus: enter <-- WHY?
//          view2 focus: enter <-- WHY?
//
//     WHY?
//
#include <gtk/gtk.h>
#include <stdio.h>
#include <string.h>

void focusEnter(GtkEventControllerFocus *ec, void *ud) { char *name = (char*)ud; printf("%s focus: enter\n", name); }
void focusLeave(GtkEventControllerFocus *ec, void *ud) { char *name = (char*)ud; printf("%s focus: leave\n", name); }
void addFocusController(GtkWidget *widget, char *name) {
    GtkEventController* ec_focus = gtk_event_controller_focus_new();
    gtk_widget_add_controller(widget, ec_focus);
    g_signal_connect_data(ec_focus, "enter", G_CALLBACK(&focusEnter), name, NULL, G_CONNECT_DEFAULT);
    g_signal_connect_data(ec_focus, "leave", G_CALLBACK(&focusLeave), name, NULL, G_CONNECT_DEFAULT);
}

GtkWidget *createTextView(char *name) {
    GtkWidget *widget = gtk_text_view_new();
    gtk_widget_set_hexpand(widget, TRUE);
    gtk_widget_set_vexpand(widget, TRUE);
    gtk_text_view_set_editable(GTK_TEXT_VIEW(widget), TRUE);
    gtk_text_view_set_cursor_visible(GTK_TEXT_VIEW(widget), TRUE);
    GtkTextBuffer *buf = gtk_text_view_get_buffer(GTK_TEXT_VIEW(widget));
    GtkTextIter endit;
    gtk_text_buffer_get_end_iter(buf, &endit);
    gtk_text_buffer_insert(buf, &endit, name, (gint)strlen(name));
    return widget;
}

void notebookEventHandler(GtkNotebook *n, GtkWidget *page, gsize idx, void *ud) { char *event = (char*)ud; printf("notebook: %s\n", event); }

static void activate(GtkApplication *app, gpointer user_data) {
    // Setup window
    GtkWidget *window = gtk_application_window_new(app);
    gtk_window_set_title(GTK_WINDOW(window), "Window");
    gtk_window_set_default_size(GTK_WINDOW(window), 600, 600);

    // Setup notebook
    GtkWidget *notebook = gtk_notebook_new();
    gtk_widget_set_vexpand(notebook, TRUE);
    gtk_widget_set_hexpand(notebook, TRUE);
    gtk_notebook_set_tab_pos(GTK_NOTEBOOK(notebook), GTK_POS_TOP);
    gtk_notebook_set_scrollable(GTK_NOTEBOOK(notebook), TRUE);
    gtk_notebook_set_show_tabs(GTK_NOTEBOOK(notebook), TRUE);
    gtk_notebook_set_show_border(GTK_NOTEBOOK(notebook), FALSE);

    char *switchPageEvent = "switch-page";
    g_signal_connect_data(notebook, switchPageEvent, G_CALLBACK(&notebookEventHandler), switchPageEvent, NULL, G_CONNECT_DEFAULT);

    // Add notebook to window
    gtk_window_set_child(GTK_WINDOW(window), GTK_WIDGET(notebook));

    // Setup Page 1
    {
        GtkWidget *box1 = gtk_box_new(GTK_ORIENTATION_VERTICAL, FALSE);
        gtk_widget_set_hexpand(box1, TRUE);
        gtk_widget_set_vexpand(box1, TRUE);
        addFocusController(box1, "box1");

        GtkWidget *view1 = createTextView("view1");
        addFocusController(view1, "view1");

        // View to box and box to notebook
        gtk_box_append(GTK_BOX(box1), view1);
        gtk_notebook_append_page(GTK_NOTEBOOK(notebook), box1, NULL);
    }

    // Setup Page 2
    {
        GtkWidget *box2 = gtk_box_new(GTK_ORIENTATION_VERTICAL, FALSE);
        gtk_widget_set_hexpand(box2, TRUE);
        gtk_widget_set_vexpand(box2, TRUE);
        addFocusController(box2, "box2");

        GtkWidget *view2 = createTextView("view2");
        addFocusController(view2, "view2");
        GtkWidget *view3 = createTextView("view3");
        addFocusController(view3, "view3");

        GtkWidget *paned = gtk_paned_new(GTK_ORIENTATION_VERTICAL);
        gtk_paned_set_start_child(GTK_PANED(paned), view2);
        gtk_paned_set_end_child(GTK_PANED(paned), view3);
        addFocusController(paned, "paned");

        // Paned to box and box to notebook
        gtk_box_append(GTK_BOX(box2), paned);
        gtk_notebook_append_page(GTK_NOTEBOOK(notebook), box2, NULL);
    }

    gtk_widget_set_visible(window, TRUE);
}

int main(int argc, char **argv) {
    GtkApplication *app;
    int status;

    app = gtk_application_new("org.gtk.example", G_APPLICATION_DEFAULT_FLAGS);
    g_signal_connect(app, "activate", G_CALLBACK(activate), NULL);
    status = g_application_run(G_APPLICATION(app), argc, argv);
    g_object_unref(app);

    return status;
}