When activating via a keyboard shortcut:

overviewVal which steps through from 0-1 
WindowHeapDelegate binds to this to update the position

We enter this step through:

        Transition {
            to: "initial, initial-hidden, active-normal, active-hidden"
            NumberAnimation {
                duration: thumb.windowHeap.animationDuration
                properties: "x, y, width, height, opacity"
                easing.type: Easing.OutCubic
            }

which will take effect at the last change making the last update look slow

and we also have a:
   TweenBehavior on x {}

which operates on all updates and also throws things off

Both of these are conflicting which gives us an animation that moves at seemingly random speeds as each X update retargets an animation badly.