Comment 0 for bug 1621509

This is the cause for the Sections index resetting after initialization, see bug https://bugs.launchpad.net/ubuntu/+source/ubuntu-ui-toolkit/+bug/1610231

Create the file ModelTest.qml:
import QtQuick 2.4

Item {
    id: root
    width: 800
    height: 600

    ListView {
        model: root.model
        onModelChanged: print("LV model changed to "+model[0]+" "+model[1]+" "+model[2]+" "+model[3])
        Component.onCompleted: print("ListView completed.")
    }
    Component.onCompleted: print("root item completed.")

    property list<QtObject> objectList
    onObjectListChanged: print("root.objectList changed to "+objectList[0]+" "+objectList[1]+" "+objectList[2])
    property var model: objectList
}

and run this program modelInst.qml:
import QtQuick 2.4
import Ubuntu.Components 1.3

ModelTest {
    QtObject {
        objectName: "one"
        id: objectOne
    }
    QtObject {
        objectName: "two"
        id: objectTwo
    }
    QtObject{
        objectName: "three"
        id: objectThree
    }

   objectList: [objectOne, objectTwo, objectThree]
}

The output is as follows:
ubuntu@xenial1:~/dev/ubuntu-ui-toolkit/m/qt56fixes2sections$ qmlscene modelInst.qml
qml: root.objectList changed to undefined undefined undefined
qml: root.objectList changed to QObject(0x118abf0, "one") undefined undefined
qml: root.objectList changed to QObject(0x118abf0, "one") QObject(0x118a110, "two") undefined
qml: root.objectList changed to QObject(0x118abf0, "one") QObject(0x118a110, "two") QObject(0x1182f80, "three")
qml: LV model changed to QObject(0x118abf0, "one") QObject(0x118a110, "two") QObject(0x1182f80, "three") undefined
qml: LV model changed to QObject(0x118abf0, "one") QObject(0x118a110, "two") QObject(0x1182f80, "three") undefined
qml: root item completed.
qml: ListView completed.
qml: LV model changed to QObject(0x118abf0, "one") QObject(0x118a110, "two") QObject(0x1182f80, "three") undefined
qml: LV model changed to QObject(0x118abf0, "one") QObject(0x118a110, "two") QObject(0x1182f80, "three") undefined

so the model ic changed AFTER the ListView and root item are completed.

When the Ubuntu.Components import is removed, the output is correct, like this:
ubuntu@xenial1:~/dev/ubuntu-ui-toolkit/m/qt56fixes2sections$ qmlscene modelInst.qml
qml: root.objectList changed to undefined undefined undefined
qml: root.objectList changed to QObject(0x171c8d0, "one") undefined undefined
qml: root.objectList changed to QObject(0x171c8d0, "one") QObject(0x171d290, "two") undefined
qml: root.objectList changed to QObject(0x171c8d0, "one") QObject(0x171d290, "two") QObject(0x171d420, "three")
qml: LV model changed to QObject(0x171c8d0, "one") QObject(0x171d290, "two") QObject(0x171d420, "three") undefined
qml: LV model changed to QObject(0x171c8d0, "one") QObject(0x171d290, "two") QObject(0x171d420, "three") undefined
qml: root item completed.
qml: ListView completed.

Also, if there is no ListView inside ModelTest.qml, then nothing is updated after the items are completed. So I suspect the issue is in our ListView extension.