How to ensure custom sort order for Managed Metadata fields is honored?

I've created a Managed Metadata term-set with the values One, Two, Three with a custom sort order as expected (1=One, 2=Two, 3=Three). But when I create a column in a list/library using this term set then try to sort the items in the list/library, they're sorted alphabetically (One, Three, Two)! This surely defeats the entire purpose of the custom sort order?

Using SP 2013.