DelegateModel + DelegateChoice = produce unexpected delegate

import QtQml.Models 2.12
import Qt.labs.qmlmodels 1.0

import QtQuick 2.12
import QtQuick.Window 2.12
import QtQuick.Controls 2.12

Window {
    visible: true
    width: 200
    height: 320

    DelegateModel {
        id: theModel

        model: ListModel {
            ListElement { role: "section" }
            ListElement { role: "item" }
            ListElement { role: "section" }
            ListElement { role: "item" }
            ListElement { role: "section" }
            ListElement { role: "item" }
            ListElement { role: "item" }
            ListElement { role: "item" }
        }

        filterOnGroup: "expanded"
        groups: DelegateModelGroup {
            name: "expanded"
        }

        delegate: DelegateChooser {
            role: "role"

            DelegateChoice {
                roleValue: "section"
                ItemDelegate {
                    text: "+ Section " + index

                    onClicked: {
                        let i = DelegateModel.itemsIndex + 1;
                        for (; i < theModel.items.count; ++i) {
                            let item = theModel.items.get(i);
                            if (item.model.role === "section")
                                break;
                            item.inExpanded = !item.inExpanded;
                        }
                    }
                }
            }

            DelegateChoice {
                roleValue: "item"
                ItemDelegate {
                    text: "Item " + index
                }
            }
        }

        Component.onCompleted: items.addGroups(0, items.count, ["expanded"])
    }

    ListView {
        anchors.fill: parent
        model: theModel
    }

}