Metasequoia 4.3.4, Win8.1 32bit, SDK 4.3.3, VS2013 Community Edition

I am writing an import plugin but cannot create child objects.

objclone->SetDepth(1) does set depth to 1 but depth is 0 after AddObject(objclone).

What am I doing wrong?

    MQObject obj = MQ_CreateObject();        
    // obj's vertices and faces are read from a file

    
    MQObject ob = MQ_CreateObject();
    doc->AddObject(ob); // add empty object
    
    for (int i = 0; i < 4; ++i)
    {
        MQObject objclone = obj->Clone();
        objclone->SetDepth(1);
        doc->AddObject(objclone); // objclone is not child of ob. Why?