Hi Andrew:
I think the Vietnamese provenance is strongly suggested from one of the pictures on this page:
http://www.sevenstarstrading.com/art...etnameseswords Towards the end of the page there is a very similar blade and a short section of the attached handle which is also similar to the mystery "panabas" on eBay.
The link comes from Scott Rodell's site at Sevenstars Trading. Thanks to Scott and Philip Tom for putting that article together.
Ian.