default property of QQmlListProperty of class in a namespace doesn't work

Invalid property assignment: "children" is a read-only property

namespace Namespace {

class SubObject : public QObject
{
    Q_OBJECT
};

class Object : public QObject
{
    Q_OBJECT
    Q_PROPERTY(QQmlListProperty<SubObject> children READ children)
    Q_CLASSINFO("DefaultProperty", "children")
...
}