Qml extention plugin as a singleton

[avkn]

My objective is to use a dynamically loaded library in Qml Quick Application project.
The library is a Qml extention plugin that exposes one object.
The problem is that this object should be a singletone.
If I include the plugin in a qml file that is declared as a singleton,
no errors at compile time, but if I try to debug, the message appears:
... Singleton.qml:6 Non-existent attached object
Is it not possible to use a class defined in QML extention plugin as a singleton? What is here wrong?

Thank you in advance for your help!