terms with slashes (/) don't lookup properly in autocomplete fields

I have an autocomplete field for a country taxonomy and type the following:

United States, Australia/Oceania

The autocomplete for both of these terms happens as expected. However, as the slash and characters following it are typed, the autocomplete continues to be for just 'Australia' as the returned list contains both the term 'Australia' and 'Australia/Oceania'.

If I continue to type:

United States, Australia/Oceania, China

I get no autocomplete for the term after the slash.

I have confirmed that the autocomplete callback is not getting anything that happens after the slash suggesting that the menu system is treating it as a different path.

The function Drupal.ACDB.prototype.search in autocomplete.js to invoking Drupal.encodeURIComponent in drupal.js to prepare the text in the field for searching.

The autocomplete system should be able to accommodate terms that contain a slash.