Items with no baseline alignment is not made visible in a RowLayout where all other items has a baseline

Add the following lines to a RowLayout in tests/manual/baselines/main.qml:

Rectangle {
    implicitWidth: 5
    Layout.fillHeight: true
    color: "red"
}

You will see that the rectangle is not visible. I would expect it to be not influenced by the baselines of its siblings, and just fill the whole height of the layout, and be 5 pixels wide.