Planet13 - 6:23 am on Jan 6, 2011 (gmt 0)
It could be a bot. Some of the preview type bots (such as those run by search engines) can cause this to occur.
Wouldn't a bot cause the bounce rate to go UP? Because it would preview the page, but not go anywhere from there?!?!?!
Oddly enough, I have another site with the same hosting software / ecommerce software and running footer GA js code, and it HASN'T seen a drop in bounce rate...