Wrong index row required in QAbstractItemModel implementation

I have complex structure of data and model to access to it.

Code:

---

Item (single value)
  |
  +-Item (single value)
      |
      +-Factory (single value)
      |   |
      |   +-Table (rows, columns)
      |
      +-Factory (single value)
          |
          +-Table (rows, columns)

---

Elements of data stored in classes inherited from BaseItem class (in QModelIndex::internalPointer). To understand which implementation of BaseItem I have in current QModelIndex I use dynamic_cast<class name>.

I return correct rowCount and columnCount for each of structure elements, but on "Factory level" row of required row is -1 (in index method). Why view (I use QTreeView) asked for index of row -1?

P.S. Code is in attachment.