I have a bow-mounted Xi3 on my kayak. The spot lock works great but when I have the motor in course lock mode it wants to wander slightly off course. For example, if I am running down a straight bank and set course lock to keep me about 20 feet from shore, it won't be long until I am heading closer or further away from the shore. It doesn't matter if it's dead calm it just doesn't want to keep straight. Anyone else have this issue? I don't know if I need to re-calibrate something or if this is considered normal variance. Since the spot lock works fine, I wouldn't think it would be an issue with the GPS receiver. Any ideas?