You may want to try asking this question with https://www.tableau.com/support/case/
This will allow someone within Tableau Support with experience using the API to respond -- it's not as likely that customers on the forum will know the answer to this one, although I welcome them to help if they can!
Thanks Matt. Will do. I just wasn't sure how deep the user community was yet so thought I'd give it a try.
Unfortunately support does not extend to the API. The response I received was that this is outside of the scope of Tableau support and my only recourse is to seek help from the community which I have. Unless you have some other ideas, it would appear as though this one is going to get chalked up as "broken in the API".