4.2 beta3 upgrade & multi-lingual: problem with triggers and option group labels

While upgrading a multi-lingual site from 4.0 to 4.2, I had the following error:

WD civicrm: $Fatal Error Details =
[...]
[code] => -19
[message] => DB Error: no such field
[mode] => 16
[debug_info] => CREATE TRIGGER civicrm_option_group_before_update before update ON civicrm_option_group FOR EACH ROW BEGIN IF NEW.label_en_US IS NOT NULL THEN IF NEW.label_fr_FR
IS NULL THEN SET NEW.label_fr_FR = NEW.label_en_US; END IF; ELSEIF NEW.label_fr_FR IS NOT NULL THEN IF NEW.label_en_US IS NULL THEN SET NEW.label_en_US = NEW.label_fr_FR; END IF; END
IF; IF NEW.description_en_US IS NOT NULL THEN IF NEW.description_fr_FR IS NULL THEN SET NEW.description_fr_FR = NEW.description_en_US; END IF; ELSEIF NEW.description_fr_FR IS NOT NULL
THEN IF NEW.description_en_US IS NULL THEN SET NEW.description_en_US = NEW.description_fr_FR; END IF; END IF; END [nativecode=1054 ** Unknown column 'label_en_US' in 'NEW']
[...]

So far, I have isolated it to the fact that CRM/Upgrade/Incremental/php/FourTwo.php calls CRM_Core_DAO::triggerRebuild(), and also that the 4.1 renames "civicrm_option_group.label" to "title".

In my database, after the error, my civicrm_option_group table has indeed renamed "label" to "title", but I wonder why triggerRebuild() is using an old schema.