Application deadlocks on exit when an item is reparented to contentItem

I implemented a custom QQuickItem and created an instance of it in QML.

The item changes change its visual parent to the window's contentItem.

When the application is closed in runs into a deadlock.

The behavior can be prevented by using a Qt::QueuedConnection but I thought, that signals are executed in the main thread so I didn't expect any threading issues here.