QtQuick Layouts columnSpan

[Uniformed6525]

Hello,

I'm trying to use a GridLayout. The latter has 3 columns and 1 row. I added two Rectangles, of respective columnSpans 2 and 1. Here's my code:

import QtQuick
import QtQuick.Layouts 1.3

GridLayout {
    id: gridLayout
    columns: 3
    rows: 1
    anchors.fill: parent
    anchors.margins: 16
    rowSpacing: 4

    Rectangle {
        Layout.columnSpan: 2
        height: 280
        color: "#111"
        Layout.fillWidth: true
    }
    Rectangle {
        Layout.columnSpan: 1
        height: 280
        color: "#111"
        Layout.fillWidth: true
    }
}

What I expected was that the first Rectangle would take up 66.6% of the available space, and the remainder would be left to the second Rectangle to use. However, instead, I get this:

If anyone can enlighten me as to why they are the same size, it would be much appreciated. Thanks in advance.