Animation FPS drops drastically during drag and drop

import QtQuick 2.4

Item {
    id: container
    width: 1000
    height: 200

    Rectangle {
        id: rect
        color: "red"
        width: 100
        height: 100

        NumberAnimation on x {
            from: 0
            to: container.width - rect.width
            duration: container.width - rect.width
            loops: Animation.Infinite
        }
    }

    Rectangle {
        id: draggedItem
        height: 100
        width: 100
        y: 100
        color: 'gray'

        Drag.active: dragArea.drag.active
        Drag.dragType: Drag.Automatic
        Drag.mimeData: {"text/uri-list": "I am being dragged"}

        MouseArea {
            id: dragArea
            anchors.fill: parent
            drag.target: draggedItem
        }
    }
}