When running the Choice Box demo FX tells JAWS it's a combo box which would indicate to the use that it's behavior is that of a combo box.

Since FX tells JAWS it's a combo box I think the UI should change to match that of a combo box, i.e. space should not open it; F4 or alt+down should.

Note from Jindra logged in RT-38532: ... since the differences in design and interaction in a choice box and combo box component are so subtle, I do not have any objection against changing the interaction to be same as in a combo box component (F4 or Alt+Up/Down to open the popup).