If there is already a question type of single choice or multiple choice and we want to load an already saved label set for it, it is impossible to do this when using the keyboard only (no mouse).

More info:
If the current question type is set to single choice or multiple choice and we press the "Load Label Set" button, it appears the dialog with the list box + drop down combo box that can be used for selecting the wanted label set. Both the list box and the combo box (that might appear as a single special control on site) appear as empty, with no choices to select.
If we press Enter or Space either on the list box or combo box to activate JAWS screen reader forms mode on, in order to try selecting an element from them, the focus is lost and moves to the beginning of the web page.
If we return to these controls and try again, they still appear as empty and can't select anything from them by using the keyboard only.