Norma,
Yeah, but I suspect the code is using the entire "tile area" as a value and then attaching a specific "reflective bounce-back this percent of light and this amount of highlight over this 32by32 pixel block" (or whatever the rendering size is), and then moving on to the adjacent portion of the screen to render.
But about a bazillion times faster, over the entire screen / display area, several times a second. Even with the camera dead-still, the virtual sun'll be moving and all those calculations will have to take place repeatedly.
As robustly as the Sims handles the display, I'm not surprised one bit some of the materials might really behave in strange fashion (especially something they may have "tweaked" for use on the ceiling, I'm sure they have a lot more "reflectivity / specularity" than other materials). It's also very possible the core values (some of the stuff we can't access even in the "Create a Style") are messed up for that particular tile. Do you see the lines when they are on the ceiling?
-- Happytime