animation behavior different when using constant property value vs direct value for duration

[Diracsbracket]

Hello,
I have an animation with a given duration (600) and a 2 parallel animations (which are sequential to each other) of duration 300 each, such that the main and last parallel animation end at the same time:

MyItem {
    id: container
    ....
    transitions: Transition {
        ParallelAnimation {
            NumberAnimation { target: rotation; properties: "angle"; duration: 600}

            SequentialAnimation {
                NumberAnimation { target: container; property: "scale"; to: 0.75; duration:  300 }
                NumberAnimation { target: container; property: "scale"; to: 1.0; duration:  300 }
            }
        }
    }
}

This works fine, but if I replace the duration by the following computed values based on a readonly property I define, the animation still works, but is different (the animations don't behave as desired: they don't end at the same time)

MyItem {
    id: container
    ....
   readonly property int animationSpeed: 600
   ....
    transitions: Transition {
        ParallelAnimation {
            NumberAnimation { target: rotation; properties: "angle"; duration: AnimationSpeed }

            SequentialAnimation {
                NumberAnimation { target: container; property: "scale"; to: 0.75; duration: animationSpeed/2 }
                NumberAnimation { target: container; property: "scale"; to: 1.0; duration: animationSpeed/2 }
            }
        }
    }
}

Why is the behavior different when I use a property value instead of a direct value for duration?

Thanks!