Whenever you edit Combobox's items list its CurrentItem is reseted to 0. It's fine, but this change isn't reflected in widgets list of properties in UI editor.

1. Create new GUI Project
2. Open MainWindow.ui and add QCombobox to it
3. Double click and add several items to combobox. Say, "a",  "b", "c".
4. Set CurrentItem property of combobox to 2
5. Double click combobox and add one more item - "d"
6. Note, that CurrentItem property is still equal to 2 - it wasn't changed
7. Save the form, close editor then open the form in editor again.
8. Note that CurrentItem property is equal to 0!