A shot in the dark, but this sounds like an export optimisation thing that was badly implemented (like the exporter saying: "Oh, I already know this texture, I won't export again to speed up the refresh), even if it's not an interactive session.
Have you tried disabling "Enable incremental export" in the Translator Tab of the render settings? Cleared the Export cache? Are you using Distributed Rendering?
I second Eugens and Erics findings of the Vray integration. The renderer is nice, but the Softimage plugin is, after all this time (4 years beta, two years on the market), still not quite production ready.
Especially export times (time to first pixel from the moment one draws a render region or presses render) is longer than with any other renderer that's currently available for Soft. The next major version is around the corner (allegedly with VrayRT support and Texture baking), so maybe that will change the situation.
Besides Redshift, it's still the only solution that gives good and fast results for interior scenes that require a lot of light bounces (unless you want to light in 3dsMax with the radiosity renderer, store global Illumination in vertex colors, transfer the geo over to XSI and render with 3Delights "SurfaceColor3DLight" vertex color feature , if you are gutsy enough to pull that sort of frankenrender off in a commercial project :-)