Consider the following QML fragment:

Rectangle
{
    color: "green"

    width: childrenRect.width
    height: childrenRect.height

    x: 100
    y: 100

    Rectangle
    {
        id: test
        color: "red"
        width: 100
        height: 50
        rotation: 45
    }
}

The expected behavior is that the green rectangle encompasses the bounds of the red rectangle. The actual behavior is that the green rectangle reflects the untransformed dimensions of the red rectangle. See the attachment for more info.

This is the simplest case I can show, but the problem exists with arbitrary hierarchies based on childrenRect. I'm working on a workaround to compute the bounds of an arbitrary child hierarchy now but I'd expect childrenRect to represent the 2D bounding box of all children regardless of transformations.