Signal can't have QML types as parameters

The documentation for adding new signals to QML says:

The options for parameter types are the same as for property types (see Adding new properties.

(at http://doc.qt.nokia.com/4.7/qml-extending-types.html#adding-new-signals)

and following the link, we see that there property can have one of the basic types, or have a type of a QML component (and also QtObject). However the following example doesn't load:

---8<--
import QtQuick 1.0

Item {
signal testSignal(int number)
signal testSignal2(QtObject obj)
}
---->8---

Is that an expected limitation of QML?