My mistake, and I should have known better: I was running projection at a Cineplex when Brother Bear came out. We received warnings with the prints that the first few minutes of the film were 1.85:1 printed anamorphic, and that the black bars at the sides of the screen were normal. This was much easier than having to switch lenses 20 minutes in, but it amplified the fact that the projected shape of the image is trapezoidal rather than rectangular.