overview: Explicitly reset parent on teardown
Instantiators create objects when they're added to a model, and deference when when they're removed from the model.
When we explicitly set a parent in onObjectAdded we're creating a second reference and taking on ownership of handling the visual parent. It's up to us to unset it to get it done by the next frame.
This brings us in line to what QQmlRepeater (which works with items) does internally for items being added and removed.
Edited by Marco Martin