From a technical point of view this is ok - but from an intuitive point of view I would think I can use persist whereever I want. So I can create an entity, persist it (so it gets written to the DB), make changes to it (like adding entities to its collection) and getting its saved (and the collection entities persisted) when I call flush().
So I suspect lifecycle events to be called whenever an entity is persisted. And in this case LifecycleCallbackTestEntity's are persisted automatically by flush() (and this is after the Cascader is persisted!), so lifecycle events should fire here.