[Update:] OK, Camino, Mozilla and Omniweb all have the same behavior. But IE on windows doesn’t do it. I’m very perplexed. I also discovered that one of my Ads is producing Pop-unders! Say goodbye to everything except Amazon.com ads.
[Update 2:] May not be Apple’s fault completely. I had the “position” of the middle box set for 10 pixels from the bottom. Apparently this means 10 pixels from what ever part of the browser window you can see.