Maybe i am off base here but it sounds like the display settings in the monitors control pannel are set at 1024x768 60hz and the display settings in the catalyst application are set to 1024x768 75hz. Thus when you boot the catalyst it changes and then when you quit it changes back. I would say you should verify that your display setting in the system os are set at what you want for your catalyst output.

Hope that helps,

Tyler