They don't. If I understand it correctly, destroying the object triggers the QEvent::Destroy event, which then goes through the event handler on the parent obje

They don't. If I understand it correctly, destroying the object triggers the QEvent::Destroy event, which then goes through the event handler on the parent object that might access that pointer. On libc++ that pointer is set to null before calling the destructor and triggering the event, so it's null pointer dereference. The object is accessed only through the unique_ptr, so unless multithreading is going on, I don't think there is a way to have use-after-free. You might be potentially accessing garbage, but it's not use-after-free. Aside, using a pointer to an object that is destroyed is not always use-after-free. Accessing the value might happen during the destruction, which is the case here or the object can be destroyed, but the memory is not released. "Placement new" and stuff.