When I issue the plot_on command to dump my objects to a file, the objects become frozen, i.e. I can't rotate them until I issue the plot_off command.

Morten replied: "There are 2 reasons that the dials become frozen:

1. When you hit plot_on, O writes the current view orientation to the file. If the dials were not frozen, you might rotate the molecule while building the plot, and become confused when the final plot has the original view.
2. The oplot file grows very quickly. Not having the dials work reminds you that the plot file is open."