When setting the tab order, it is possible to go from a container widget (such as a tab widget) into a widget that is inside it. This can cause problems as the tab order should not be set from a container widget into a widget that is in it.

To reproduce:

• Add a QTabWidget to the blank widget
• Add a QDoubleSpinBox to the page inside the QTabWidget
• Enter Tab Order mode

It will allow you to set the order to be the QTabWidget and then the QDoubleSpinBox will cause problems when tabbing. Ideally it will not allow the tab order to be set in this manner, or considering the changes that were made that means that this is not straightforward to do in Qt Designer anymore, maybe the functionality should be removed.