As far as I can tell, any object which has single-face material assignments is susceptible to this bug. Several test cubes in the same scene will all display the same error.

I was blethering on about how unlikely this was to occur in "real life" when I realised that one of my most-used props was made this way. I use my Basic Box prop in nearly every scene, at least as a set-up aid which is deleted later, and sometimes it forms the background with suitable materials applied. The three walls and the floor are all single polygons.

On trying it out, I found that, as might be predicted, preview wouldn't display colour changes to the back wall material (which is the first usemtl in the geometry file), and that changes to the right wall (the second assignment) are repeated on the back wall. Everything renders properly, as previously noted. I'd never seen it before since I never apply plain colour to the box walls; it's always an image map of some sort if it stays in the scene at all.

With that in mind, it's odd that the preview would handle (relatively) complex stuff like image mapping, but not simple-seeming stuff like colour. What's more, once maps have been applied, the faces can be coloured and preview properly! That's an anti-aliased preview posted above.

Poser, you are awful, but we like you. :-)

(Edited for clarity)