### Godot version

4.1.1

### System information

linux

### Issue description

[simplescreenrecorder-2023-08-30_15.01.51.webm](https://github.com/godotengine/godot-proposals/assets/71937306/537d92b9-4f98-4fe6-adf4-71297be0471a)

I guess this wasn't the case before since I could save a layout named "2 monitors".

### Steps to reproduce

press space

### Minimal reproduction project

none
List<StringName> names;
	Ref<Theme> old_snapshot = edited_theme->duplicate();
	Ref<Theme> new_snapshot = edited_theme->duplicate();
	EditorUndoRedoManager *ur = EditorUndoRedoManager::get_singleton();
	ur->create_action(TTR("Remove Data Type Items From Theme"));
	new_snapshot->get_theme_item_list(p_data_type, p_item_type, &names);
	for (const StringName &E : names) {
		new_snapshot->clear_theme_item(p_data_type, E, edited_item_type);
		if (p_data_type == Theme::DATA_TYPE_STYLEBOX && theme_type_editor->is_stylebox_pinned(edited_theme->get_stylebox(E, p_item_type))) {
			ur->add_do_method(theme_type_editor, "_unpin_leading_stylebox");
			ur->add_undo_method(theme_type_editor, "_pin_leading_stylebox", E, edited_theme->get_stylebox(E, p_item_type));
		}
	}
	ur->add_do_method(*edited_theme, "clear");
	ur->add_do_method(*edited_theme, "merge_with", new_snapshot);
	ur->add_undo_method(*edited_theme, "merge_with", old_snapshot);
	ur->add_do_method(theme_type_editor, "_update_edit_item_tree", edited_item_type);
	ur->add_undo_method(theme_type_editor, "_update_edit_item_tree", edited_item_type);
	ur->commit_action();
}
void ThemeItemEditorDialog::_remove_class_items() {