Case sensitive taxonomy terms

When importing terms with "create_term" enabled, case-variations on existing terms result in both the existing term (with the wrong case) and a new term (with the correct, updated case) being added to the taxonomy term reference field.

In my migration, I have:

 $this->addFieldMapping('field_term_topic', 'topic')
   ->description(t('Topic'))
   ->arguments(array('create_term' => TRUE));

I have an existing taxonomy term named "Social conditions", but the migration data now has the term "Social Conditions".

Both terms get included in the migrated field because the database query that gathers existing terms is case-insensitive; a new term is created if there is no exact case-sensitive match found, but all matches are ultimately added to the field. In my case, the field will contain both "Social conditions" and "Social Conditions", even though only the latter is specified in the data.

I'll post a patch shortly.