QML Layout does not scale children correctly when they are initially hidden

I have a RowLayout with multiple children which I want evenly distributed over the available space. Some of these are initially hidden and will be shown at runtime.

Example scenario:
2 rectangles, 'blue' one initially hidden. Clicking on the 'red' one makes the 'blue' rectangle visible.

Expected: Both rectangles should then evenly use the space.
Actual: Only 'red' rectangle is visible + spacing. 'Blue' rectangle remains hidden.

RowLayout {
    anchors.fill: parent

    Rectangle {
        id: rect1
        Layout.fillWidth: true
        Layout.fillHeight: true
        color: "red"

        MouseArea
        {
            anchors.fill: parent
            onClicked:
            {
                rect2.visible = !rect2.visible
            }
        }
    }

    Rectangle {
        id: rect2
        Layout.fillWidth: true
        Layout.fillHeight: true
        color: "blue"
        visible: false

    }
}

Setting preferredWidth on both as suggested here https://bugreports.qt.io/browse/QTBUG-43261 does not help.

Attached is example code, click on red rectangle to try make the blue one visible (which won't work).