Q_ENUM value undefined in QML Connections object

Scenario:

Qt Quick 2 based app, with a C++ QObject (named Proxy) which acts as a signal/slot proxy between QML and C++.

The object is registered into QML with qmlRegisterUncreatableType<Proxy>(...) (or qmlRegisterType<Proxy>(...), it doesn't make a difference).

The object defines an enum Proxy::MyEnum, registered with Q_ENUM, and also with qRegisterMetaType<Proxy::MyEnum>(), and also respecting the convention of having the enum items starting with a capital letter, 

At application startup, in C++, a context property is set to hold the instance of the Proxy object; also, the QML object defining the signals is found, and is connected to the respective slots of Proxy. In QML there is a Connections object which connects to the signals emitted by Proxy.

Issue:

At runtime, on QML side, Proxy.EnumValue is defined in handlers such as Component.onCompleted, Button.onClicked, but it is undefined in Connections.onFooChanged.

Repository with minimal test case: https://github.com/fferri/qml-enums.git

Testcase output on my machine: 

qml: Component.onCompleted: Proxy.EnumValue = 20
qml: testButton.onClicked: Proxy.EnumValue = 20
Proxy::initFoos
qml: Connections.onFooChanged: index = 0, e = 20, v = 100
qml: Connections.onFooChanged: Proxy.EnumValue = undefined
qml: Connections.onFooChanged: index = 1, e = 21, v = 550
qml: Connections.onFooChanged: Proxy.EnumValue = undefined