Check your perspective angle. Select your 3D object and look inside the Properties Panel's 3D Position and View section. Perspective Angle has a little camera icon. The default for a 550px by 400px image is 55.0.
When you resize the stage this angle will change. I'm not sure why it changes in new file also. Did you use the same object in the new file? A lot of time 3D settings might still be saved with the object even after you remove the tween.
Flash Pro, QE
Thanks for your reply! I finally realized what I did wrong. Evidently, the motion presets (or at least the one for the zoom in 3D) are designed only to work with the default stage size. I had changed my stage size, so the preset's numbers were all off. But it's okay--I used it as a model to create my own motion, and it came out great.