Reverse the Force Feedback like I said and it should fix it. I doubt Logitech sell dodgy wheels as I've had my G27 for a few months and never had any problems because I had a G25 before and my settings carried over. Logitech wheels have an issue where you need to reverse the Force Feedback or else you'll get the problem you're talking about.
ISI released an updated EXE that adds support for the G27 LEDs and also reverses the reversed FFB. So if you have the old EXE then you need your FFB set to -100. If you have the new EXE you set the force to +100.