I have a feeling that the conflict may be with Ceon Advanced Shipper. Can your fix for Ceon URI mapping also be made to work with Advanced Shipper?
Because I do not have, I think that it is impossible.
http://www.s-page.net/en/
I develop the module which Zen-Cart integrates with other CMS. (WordPress and XOOPS)
It may be funny English, but please endure it. (I am weak in English)