Please describe the problem:
If the current line in 'Theme selection tree' table is the first line and user
hit <down>, the second line will be the current one but gnopernicus won't report it.
This is because there is no "object:active-descendant-changed" at-spi event
fired  in this situation. 
The events received are:
  "object:selection-changed" for 'table'
  "object:visible-data-changed" for 'table'
These events should be followed by an "object:active-descendant-changed" event
in order to have the description of the current line.  

Steps to reproduce:
1. 
2. 
3. 


Actual results:


Expected results:


Does this happen every time?
yes

Other information:
The lack of this event is present only if user moves from 1st line to 2nd line.
If user moves back to 1st line (hit <up>) or forward to 3rd line (hit <down>)
this event is fired and gnopernicus outputs the description for the current
table line.