KComboBox's KLineEdit drawn with no border at all when KComboBox::setEditable(true) is called on already visible widget

After this change 2f351fe1 KComboBox's KLineEdit is drawn with no border at all (see picture)
when KComboBox::setEditable(true) is called on already visible KComboBox widget.

To reproduce you can apply this Pull Request frameworks/kio!245 to KIO
and run KWrite (or anything), click Open to show KFileWidget, and then double-click on 'Type filter' KComboBox widget.
Connecting any signal to KIO's d->filterWidget->setEditable(true) will have the same effect.

To reproduce you can apply this simple commit to pdabrowski/kio@50d749cb to KIO
and run KWrite (or anything), click Open to show KFileWidget, and then press Alt+AnyKey shortcut to make 'Type filter' KComboBox widget editable.

With 2f351fe1 reverted the above works fine.

All other styles ("Oxygen", "Fusion", "MS Windows 9x") work fine.