Event sent from C++ to QML (signal->Connection) is not destroyed (its copy, actually)

Hello.
I am sending a class through a signal, that is received by a QML page.
To do so:

• I declare the class : Q_GADGET EvTest( QString ) (Q_OBJECT gives a similar but different problem, see below)
• register it: qRegisterMetaType< EvTest >( "EvTest" );
• Create a Qml window through a C++ class QmlWidget (inheriting from QQuickWidget), that reads in main.qml
• make a connection in main.qml: Connections { onSigTestToQml: print("I received an event", event ) }
• emit a signal: emit( sigTestToQml( EvTest( "event_to_qml" ) ) )
  -> the signal is properly received and read by the qml page

But what happens is that the event created is duplicated twice (copy constructor) (why not), and also calls an empty constructor of EvTest (why?). The real problem is that the second copy of the event is never destroyed. Also, the event strangely created from the empty constructor is only destroyed at the very end of the program.

If instead EvTest inherits from QObject (using Q_OBJECT), the empty constructor is not called (seems good), only one copy of the Event is called; but still, this copy is not destroyed.

In the unit test (enclosed), I verify that sending and catching the same signal, but from a normal QObject (not a QQuickWidget), there is no problem of destruction. The test with QQuickWidget fails.

In a nutshell: sending a class to QML creates copy of that class and does not destroy the copies properly, from what I saw. If the QML doesn't catch/connect to the signal, there is no problem.

I didn't try with more versions of Qt than 5.6.0 and 5.5.1.
Thank you.

Summary of output:
EvTest is a Q_GADGET, sent to Qml:
+ Creating 'original'
+ Copying -> copy_of_original
+ Creating EvTest empty!! (why?)
+ Copying -> copy_of_copy_of_original
- Deleting 'copy_of_original'
- Deleting 'original'
qml: QML Widget received a signal EvTest 'copy_of_copy_of_original'
- Deleting 'Empty'
-> never deleting 'copy_of_copy_of_original'

EvTest is a Q_OBJECT, sent to QML:
+ Creating 'original'
+ Copying -> copy_of_original
- Deleting 'original'
qml: QML Widget received a signal undefined
-> never deleting 'copy_of_original'

Event sent to a QObject:
+ Creating 'original'
+ Copying -> copy_of_original
Received test EvTest 'copy_of_original'
- Deleting 'copy_of_original'
- Deleting 'original'
-> OK