`KExtraColumnsProxyModel::extraColumnData()` and `KExtraColumnsProxyModel::setExtraColumnData()` are receiving a `index.parent()` but they might be receiving the same `index` passed to `KExtraColumnsProxyModel::data()` and `KExtraColumnsProxyModel::setData()`.

I see no reason why the interface would be called with an invalid parent index for example. Here is my suggestion for the fix :

```cpp
QVariant KExtraColumnsProxyModel::data(const QModelIndex &index, int role) const
{
    Q_D(const KExtraColumnsProxyModel);
    const int extraCol = extraColumnForProxyColumn(index.column());
    if (extraCol >= 0 && !d->m_extraHeaders.isEmpty()) {
        return extraColumnData(/*index.parent()*/ index, index.row(), extraCol, role);
    }
    return sourceModel()->data(mapToSource(index), role);
}
```

```cpp
bool KExtraColumnsProxyModel::setData(const QModelIndex &index, const QVariant &value, int role)
{
    Q_D(const KExtraColumnsProxyModel);
    const int extraCol = extraColumnForProxyColumn(index.column());
    if (extraCol >= 0 && !d->m_extraHeaders.isEmpty()) {
        return setExtraColumnData(/*index.parent()*/index, index.row(), extraCol, value, role);
    }
    return sourceModel()->setData(mapToSource(index), value, role);
}
```