Can I use a gradient with a Qt Location MapPolygon?

Question

I have a Qt Location map upon which I'd like to draw some polygons. The MapPolygon class provides an easy way to drape a polygon over the terrain, as desired. I would like to shade the polygon using a gradient, like RadialGradient.

I'm playing with the Map Viewer example application in Qt 5.9. I edited the map/MapComponent.qml QML file and added the following item to the map:

MapCircle {
    center {
        latitude: -27.5
        longitude: 153.0
    }
    radius: 5000.0
    border.width: 0
    RadialGradient {
            anchors.fill: parent
            gradient: Gradient {
                GradientStop { position: 0.0; color: "red" }
                GradientStop { position: 0.25; color: "red" }
                GradientStop { position: 0.5; color: Qt.rgba(0, 0, 0, 0) }
            }
        }
}

The documentation for MapCircle indicates that it uses MapPolygon under the hood, so I'm using it here for simplicity. If I run the test application, the gradient seems to work:

This is what I would like. However, if I scroll the viewport so that part of the circle is clipped out of the viewable area, the gradient doesn't look right:

Here's what appears to be happening to me:

• When the circle is clipped partially offscreen, it adjusts its bounding box to reflect the portion of the screen that it covers.

• Since the gradient is anchored to the parent MapCircle object, it automatically stretches its size to cover the clipped bounding box.

• This results in the entire radial gradient shape being rendered in the compressed bounding box, which is not what I want. I want the gradient object's geometry to stay attached to the circle's true size and location. Instead of the compressed gradient that I see in the second picture, I want to see a similarly-clipped portion of the original radial gradient.

Is this possible with Qt 5.9? It's not clear to me whether this is a rendering bug, or if it's just not intended to be usable this way.