The attached example sets the sourceComponent through the states property in a Loader. This component is created twice on initialization and will never be destructed.
It is also active and could receive signals etc.

The behavior could be examined by just loading main.qml.
There you get the log message from line 52 twice. You also get two messages by pressing the triggerSomething button which emits a signal that the component consumes(plots a message).

This behavior is tricky and could be fixed by activiting the Loader in Component.onCompleted.