I have copied this from my Optimizing GIFs tutorial, "You may need to UNcheck the Write Minimal Frames box or your animated parts might leave a trail or ghost (this is part of the image that is carried over when one frame changes to the next)."
If you look at the example tag, the animation has a trail in a few frames. Uncheck the write minimal frames box when you animate this unless you are creating your tag on a solid white background, then this does not apply; only for transparent background.