The focused group change check had several issues:

 - The `prevFocused` variable was not updated after the focused group
   changed, so the `GROUP_FOCUSED` event was emitted every time the app
   state changed.

 - Groups were compared by reference rather than by ID, which means that
   a change which modified a property of the group but not its ID would
   cause the event to fire.

The first issue made it impossible to create annotations because the
unnecessary `GROUP_FOCUSED` event triggered a cascade of reactions which
crashed the app.