Depends how hard you are pressing on it mate. Also, depends on what pad you are using too. It's easier to stop it spinning while using a finishing pad on the body. Some people draw a line on the yellow part of the backing plate so they can be totally sure it's actually turning and not just vibrating.
The G220 can cause a bit of an optical illusion at times as it doesn't stick to a perfect rotation - it's random oribital to some extent so as to not inflict too much damage for the average new user.