Sum function not available for "Any vote result" condition

Very strange, this problem doesn't happen on my home PC where I run a test drupal installation, but it happens on my live web hosted drupal where I am running exactly the same modules.

I want to promote a node to front page when it gets more than X votes, from the vote_up_down module. On my home PC, I set the condition for "Any vote result" to
Points - Vote - Sum - Is greater than or equal to - X
That works fine.

On my web hosted setup, the Sum function did not appear as an option in the third box. After some grepping, I found nothing using the word Sum, but line 209 of voting_actions.inc shows:
> '#options' => _voting_actions_table_values('function', 'cache', array('' => t('--'), 'average' => t('Average'), 'count' => t('Count'))),
This seems to control the options that show up in that third box. If I add 'sum' => t('Sum') to this array, my web hosted setup works just like at home.

Any idea what happened here? Why is my home setup showing an option in that third box (Sum) that doesn't seem to exist in the code?