A3.11 Objects Rotate Strangely or Appear Distorted
Adding additional objects may change the proportions of the current objects in the model. For the first object created in the model, the model range does not need to be the same in each direction. If you wish to include more than one object in a model, however, it is important that the model range has the same linear extent in each direction. This is a problem only if the model range has been changed manually.
The default point of rotation has been changed in Dynamic Visualizer's preferences. Choose Mathematica Graphics... in the Edit menu to change the default point of rotation or explicitly set the point of rotation in Mathematica when building complex models.