Regression [5.7.1 -> 5.9.1] Changing a QML singleton creates a cache issue leading to undefined behaviours

pragma Singleton
import QtQuick 2.7

QtObject
{
    id : themePalette
    property color textColor : "red"
}

main.qml :

import QtQuick 2.7
import QtQuick.Controls 2.0
import QtQuick.Layouts 1.0
import QtGraphicalEffects 1.0
import QtQml.Models 2.1
import UIComponents 1.0

ApplicationWindow {
    visible: true
    width: 800
    height: 900
    title: qsTr("EOS Designer")

    Rectangle {
        color : UIPalette.textColor
        anchors.fill : parent

    }
}

pragma Singleton
import QtQuick 2.7

QtObject
{
    id : themePalette
    property color anotherproperty : "blue"
    property color textColor : "red"
}