Strange and inconsistent behavior for grouped properties

Run the code below. Note that it works as expected.

1) Comment in the //1 line and run again. Note how it is never called. Defect?
2) Comment in the //2 line and run again. This results in: Cannot assign to non-existent property "onPixelSizeChanged"
3) Change the //3 line to "font: {" and run again. Note how the onPixelSizeChanged is called, but the pixelSize is not set and an error is printed: Unable to assign [undefined] to QFont font

import Qt 4.7

Rectangle {
    width: 800
    height: 480

    TextInput {
        id: textInput
        anchors {
            fill: parent
            margins: 100
//1            onMarginsChanged: print("Margins changed: " + anchors.margins)
        }

        font {   //3
            pixelSize: 20
//2            onPixelSizeChanged: print("Font size changed: " + font.pixelSize)
        }

        text: "Hello world!"
    }
}