QML scenegraph asserts when a Text element is given an image with size specified as "px"

import QtQuick 2.0

Item {
    width: 300
    height: 200

    Text {
        anchors.centerIn: parent
        textFormat: Text.RichText

        //this asserts:
        //  ASSERT: "!m_targetRect.isEmpty()" in file scenegraph\qsgdefaultimagenode.cpp, line 334
        text: '<img src="http://store.qt.io/Global/About%20Us/Qt_master_logo_CMYK_300dpi.png" align="left" width="50px"/>'

        //This works (no "px" specified for width):
        //text: '<img src="http://store.qt.io/Global/About%20Us/Qt_master_logo_CMYK_300dpi.png" align="left" width="50"/>'
    }
}