Second level index does not know where it is in the site

I am really impressed with Vocabulary Index but I am having a weird problem. Let's say I have a taxonomy with terms like this....

+Operating Systems
- Windows
+ Linux
- Ubuntu
- Fedora
- Gentoo
- Macintosh

The Index for Operating Systems is fine. The navigation expands correctly and the breadcrumbing is right. The Index page for Linux has the correct content but the navigation does not expand and the breadcrumbing just says Home->Linux instead of Home->Operating Systems->Linux.

When I turn Vocabulary Index off the page has the correct breadcrumbing and navigation action, so it is clear to me that it is a problem with Vocabulary Index.