Help /taxonomy/term/<tid> failing when term created in a certain way

this is a real scull scratcher for me.
I have been doing a database migration from an old mambo CMS.

Everything goes fine... the nodes get created in two languages, the relationships between translated nodes is preserverved, the mambo tags get transformed into drupal taxonomy terms.... all great.

But then...
For the content in spanish, I have to transform the terms into new spanish tags.

my process goes something like this.

I create the vocabularies
I create the english terms, including adding entries in the term_hierarchy that indicates a flat hierarchy
I then populate term_node for all content (english and spanish)
I then populate term_data with the spanish terms (if I do this sooner, then the spanish and english terms collide because there is overlap)
I have a query that looks for spanish nodes, then translates the terms to spanish terms.
I then update term_node for those spanish nodes and replace english terms with spanish terms (tid's).

When I look for content through the admin interface by one of the spanish terms, no problem.
When I view content I see the spanish tags, no problem.
When I click on the spanish tag, without fail, /taxonomy/term/586, returns no results, even though I just came through a listing of content with that term.

Any thoughts??
I've tried disabling Taxonomy Translation, but no help.

Does anyone know how Taxonomy Translation works in the database? I couldn't make sense of the i18n and locale schemas, they do a lot with a few fields. Is that a red herring?

Is there some other tables I should be looking at in the database besides the term_ tables and vocabulary?

Thanks for any help you might have.