ListView.snapMode doesn't work correctly with header item.

import QtQuick 2.12
import QtQuick.Controls 2.5

Item {
    id: root
    width: 640
    height: 480

    ListView {
        id: list
        anchors.fill: parent
        model: 10
        header: Rectangle {
            width: 640
            height: 50
            color: "green"
            z: 11
            opacity: 0.5
        }
        headerPositioning: ListView.OverlayHeader
        spacing: 50
        snapMode: ListView.SnapToItem
        delegate: Rectangle {
            width: 640
            height: 100
            color: "red"
        }
    }

    Button {
        font.pixelSize: 20
        text: list.contentY.toFixed(0)
        onClicked: {
            list.returnToBounds()
        }
    }
}