I have a Wordpress blog with an iframe on the sidebar, and the same code is rendering a different height in IE9. The website is at http://office-porn.net/ (NO ADULT CONTENT). Does anybody know where is it coming from? Thank you.
It looks like you removed that section from your sidebar so I can't offer you any help. My first guess would be to use the max-height css property to solve the issue. It seems that your post and page redirects are broken now, you should go into the WP admin panel and regenerate your permalinks to fix it.
When I check with Chrome and IE9 webmaster tools, both iframes display the same height 4701px. They just look differently in these browsers. The website is still at http://office-porn.net/ Thank you.
If it bothers you, read about the box model hack. CSS can mung up anything you like. (A given user will almost always be using the same browser, so he'll always see the same display. If it works in IE [I can't see anything wrong with it in IE], just leave it.)