It correctly warns that is will do so but expected behavior is to delete the instance only.
Console output
QAbstractItemModel::endRemoveRows: Invalid index ( 0 , 3 ) in model QmitkMultiLabelTreeModel(0x2316bbd87d0) QAbstractItemModel::endRemoveRows: Invalid index ( 0 , 0 ) in model QmitkMultiLabelTreeModel(0x2316bbd87d0)