Check boxes not checkable with VoiceOver

VoiceOver cannot check checkboxes or radio buttons on OS X.

Steps to reproduce:
1. Launch examples/widgets/widgets/groupbox/groupbox.app
2. Launch VoiceOver (Cmd-F5)

(radio buttons: )
3. Move VoiceOver cursor to the "Exclusive radio buttons" group (VO-left/right)
4. Interact with the group (VO-Shift-down)
5. Move VoiceOver cursor to the "Radio button 2" radio button (VO-right), verifying it is not set (and only "Radio button 1" is set out of the 3)
6. Select the radio button (VO-Space)

(check boxes: )
7. Stop interacting with the "Exclusive radio buttons" group (VO-Shift-up)
8. Move VoiceOver cursor to the "Non-Exclusive Checkboxes" group (VO-left/right)
9. Interact with the group (VO-Shift-down)
10. Move VoiceOver cursor to the "Checkbox 1" radio button (VO-right), verifying it is unchecked
11. Press the "Checkbox 1" checkbox (VO-Space)

Expected Behavior:
After step 6.: "Radio button 2" becomes set and "Radio button 1" becomes unset, all other window elements remain unchanged
After step 11.: "Checkbox 1" becomes checked, all other window elements remain unchanged

Actual Behavior:
After step 6.: no change at all
After step 11.: no change at all

Workaround:
Click the checkbox/radio button using mouse, that is:
1. Move mouse to VoiceOver cursor (VO-Cmd-F5)
2. Click mouse (VO-Shift-Space)