It is very easy to click on the ad as the page refreshes the different sized text blocks - could this be what ultimately your design has been optimised for?
If the CTR is too high or completion rate is too low, you are likely to be banned, no matter what the Adsense TOS say. See this thread for comparison: http://news.ycombinator.com/item?id=2049105
Nothing in adsense TOS says that doing that is wrong.
The reason why I keep asking about adsense TOS compliance is that if you get banned for click fraud, you don't get to keep all of your earnings to date - Google can and will not pay you for anything that isn't in your bank account, trust me on this ;)