Customized Qt.labs ComboBox won't display in an asynchronous Loader

I'm trying out the Technical Preview of the QtQuick.Controls 2.0 known at the moment as Qt.labs.controls 1.0.

As you can easily customize those new controls, putting a customized ComboBox in an asynchronous Loader makes it to not appear at all, printing this message in the console :

qrc:/main.qml: Object destroyed during incubation

This is quite inconvenient as a similar bug existed in Qt 5.5.0.
This might be related to this unresolved bug (Controls 1.0)

I found out that customizing any of the available properties (even separately) triggers the bug, exception for delegate.

Here's minimal code to reproduce the bug :

import QtQuick 2.6
import Qt.labs.controls 1.0

ApplicationWindow {
    id: root
    visible : true
    width   : 640
    height  : 480

    property bool  triggerTheBug: true // Swap this to see a normal display of the ComboBox

    StackView {
        id: myStackView
        anchors.fill: parent
        initialItem: Loader {
            anchors.fill: parent
            asynchronous    : triggerTheBug
            sourceComponent :
                ComboBox { popup      : Popup{} }         // BUG
            //ComboBox { background : Rectangle{} }     // BUG
            //ComboBox { contentItem: Rectangle{} }     // BUG
            //ComboBox { delegate   : ItemDelegate{} }  // NO BUG
        }
    }
}

I attached a .zip file with extended code proving that my customizations works well when using a standard Loader.

If you try out the attached example, you'll also notice that for a standard ComboBox in an asynchronous Loader, the first element of the model won't show upon completion of the component, you need to select it yourself.