Steps to reproduce the problem:
(1) Open ADS, close all tabs and exit ADS.
(2) Reopen ADS, no tabs displayed in tabbed pane.
(3) Launch Query Analyzer from any valid server, let's say the server name is 'SN'.
(4) Repeat step #3 for 4 more times.
Now, ADS should have the following tabs displayed:
  'SN [Untitled]'
  'SN [Untitled 2]'
  'SN [Untitled 3]'
  'SN [Untitled 4]'
  'SN [Untitled 5]'
(5) Close 'SN [Untitled 2]' and 'SN [Untitled 3].
Now, ADS should have the following tabs displayed:
  'SN [Untitled]'
  'SN [Untitled 4]'
  'SN [Untitled 5]'
(6) Close ADS and reopen ADS.
The following tabs displayed in ADS
  'SN [Untitled]'
  'SN [Untitled 2]'
  'SN [Untitled 3]'
but not
  'SN [Untitled]'
  'SN [Untitled 4]'
  'SN [Untitled 5]'

In the current ADS implementation, ADS did not restore tab's title; tab titles are generated implicitly. No sure if this is by design or not.