[Orgmode] Hierarchical checkbox summary works on one machine but not another

[Charles Cave]

The following hierarchical list structure has checkbox
statistics "cookies" at a top level as well as the 2nd level.

I use org-mode 6.34 on Windows XP on both my home and office PCs.

I am stumped that the following structure updates the cookies
correctly on  my work machine as follows.....

+ Total Food [6/8]
   1. Fruit [3/3]
      - [X]  Bananas
      - [X] Oranges
      - [X] Grapes
   2. Vegetables [1/2]
      - [X] Carrots 
      - [ ] Potatoes
   3. Drinks [2/3]
      - [X] Water
      - [ ] Coffee
      - [X] Wine

....but ignores the structure on the home computer:

+ Total Food [3/3]   <--- should say [6/8]
   1. Fruit [3/3]
      - [X]  Bananas
      - [X] Oranges
      - [X] Grapes
   2. Vegetables [2/2]
      - [X] Carrots 
      - [X] Potatoes
   3. Drinks [3/3]
      - [X] Water
      - [X] Coffee
      - [X] Wine


I cleaned out the elisp folder on the home machine and reinstalled
org-mode, but I can't understand the difference.  Is there
a customisation variable apart from org-hierarchical-checkbox-statistics?

Thakns
Charles