Loading components asynchronously is not working correctly

This bug is likely related to QTBUG-36826.

Steps to reproduce:
1. run: qmlscene main.qml
this will show 1 red rectangle in upper left corner (should be 10)
2. close the window

This will print message in console:
"There are still "9" items in the process of being created at engine destruction."

When setting asynchronous to false in main.qml, this works as expected. Also works if using for example Timer to run init function instead of using Component.onCompleted