QIdentityProxyModel does not properly handle/propagate 'layoutAboutToBeChanged' signal from the source model.
In particular it stores it's persistent index list before emitting the layoutAboutToBeChanged signal and therefore before an attached views can actually store/retrieve the persistent indexes from the model. This (among other things) breaks item view's selection when sorting the source model.

The fix should be simple, just move the q->layoutAboutToBeChanged(); line in QIdentityProxyModelPrivate::_q_sourceLayoutAboutToBeChanged
before the for loop.