sub-directory namespace underlined as 'unknown type' in QML editor

How to reproduce

Open $CREATORDIR/tests/manual/qml/testfiles/usingbutton.qml:

import Qt 4.7
import "components" as X

Rectangle {
    width: 640
    height: 480

    X.MyButton {
    }

}

The 'X' in 'X.MyButton' is underlined, and the tooltip shows 'unknown type'. This can be fixed by loading MyButton.qml once in the editor.