PropertyAnimation on rotation degrades as user continuously stops/starts animation

Continuously starting and stopping the animation will see the rotation period decrease.

import Qt 4.7

Item {
width: 640
height: 360
Rectangle {
anchors.centerIn: parent
width: 10
height: 50
color: "grey"
PropertyAnimation on rotation

{ id:spinnerAnimation; to: 360; duration: 600; loops: Animation.Infinite }

}
MouseArea

{ id: mouseArea anchors.fill: parent onClicked: spinnerAnimation.running = !spinnerAnimation.running onPressAndHold: Qt.quit() }

}