QUOTE: So it seems to me that while you can turn off the PE, you don't unregister the object and somewhere, it's velocity is stored and thus when the engine is re-engaged, it loads up these old values for velocity and goes from there.

You're right. I've got a PE that constantly orbits around a center. With each frame I turn off/on phent_enable to readjust its pan, and it moves on without the orbiting force renewed. Frankly, the readjusting of the panning doesn't seem to be smooth, despite a high frame rate. Maybe phent_settype ( entity, 0, var hull disengages correctly.