KeyframeGroup assign property even animation didn't start

import QtQuick
import QtQuick.Controls
import QtQuick.Timeline

Rectangle {
    id: root
    color: "#000000"
    width: 800
    height: 480

    Timeline {
        enabled: true
        animations: [
            TimelineAnimation {
                id: test
                duration: 33 * 60
                from: 0
                to: 60
                onStarted: console.log("TimelineAnimation onStarted")
            }
        ]
        KeyframeGroup {
            target: testitem
            property: "testProperty"
            Keyframe { frame: 0; value: "123123213" }
        }
    }

    Item {
        id: testitem
        property string testProperty
        onTestPropertyChanged: console.log("testProperty:", testProperty)
    }
}