My expereince is as far as i dont use the IPR rendering option, the swatches of the material display remains and i can play with the settings and see the changes.

You can try it.
Create a poly sphere. Assign any mental ray material say a car paint shader. Render it in mental ray. Now click on the IPR window. It should change to a wireframe image. Now click drag a window anywhere. Now try to change the color of the material. The swatch will change to maya logo.

Check if that happens on your pc too. Would like to know.

Mahesh