Hi adwb,
I use the fs8 copilot on my airplane to help teach myself to fly. The feature that is causing your problem is the Auto Trim. This functions even when the gain is down to 0% as default, but you can easily turn it off. See page 18 of the FS8 reference manual. You need to turn this off. To change Auto Trim from on to off or vise versa, simply push the Receiver button 6 times while in the normal flight mode and then turn off the copilot by disconnecting the battery.