void QSortFilterProxyModelPrivate::sort()
{
...
    emit q->layoutChanged(QList<QPersistentModelIndex>(), QAbstractItemModel::VerticalSortHint);
}

After this, the TableView does not immediately reorder the delegates, but flicking back and forth will make it do that.

A workaround is in my QSortFilterProxyModel subclass (which is necessary mainly because sort() is not Q_INVOKABLE), I can use beginResetModel(); sort(); endResetModel();