QComboBox::setModel uses an invalid root for setting the current index.

In the QComboBox::setModel method, the root model index (d->root) can be invalid. Not invalid according to the isValid() method. Not invalid due to some changes inside the model since it is a QPersistentModelIndex. But invalid, because the model and the index aren't even semantically linked.

If someone creates a QComboBox, attach a model to it with setModel, change the root model index with setRootModelIndex and later update the model with setModel, the root index can mismatch this new model. I guess the expected behaviour is to reinitialize the root index every time the model is updated.