When propagateComposedEvents is set, drag does not always move the flickable

import QtQuick 2.1
import QtQuick.Window 2.0

Rectangle
{
    id: mainScreen
    width: 400
    height: 400

    color: "darkgray"

    // main grid
    Flickable{
        id: gridflick
        interactive: true
        anchors.fill: parent
        contentWidth: 900
        contentHeight: 900

        Column{
            id: grid
            x: 10
            y: 10
            spacing: 10
            Repeater{
                model: 5
                Row{
                    height: 80
                    spacing: 10
                    Repeater{
                        model: 5
                        Rectangle{
                            color: "steelblue"
                            id: panel

                            width: 80
                            height: 80
                            MouseArea{
                                anchors.fill: parent
                                propagateComposedEvents: true
                                onClicked:{
                                    console.log("clicked")
                                }
                                onPressAndHold: {
                                    console.log("press and hold")
                                    // mouse.accepted = false
                                }
                                onPressed: {
                                    console.log("pressed")
                                }
                            }
                        }
                    }
                }
            }
        }

        onMovementEnded: {
            console.log(" onMovementEnded")
        }
        onMovementStarted: {
            console.log("onMovementStarted")
        }
    }

    focus: true
}