My company provides a property listing service that is implemented via javascript and an iframe. This particular case is a lot more customized than most, passing variables from our site to their URI for more seamless integration (usually we just pass all URI variables in the iframe).
Here's the unexpected bit... seemingly at random the footer is duplicated at the bottom of the iframe, yet the tag is closed propperly. It happens across IE6 and FireFox2, I haven't had it happen in IE7 and I haven't tested it in Safari... but it's mindbogglingly annoying and I think it's Javascript/DOM related. However I am woefully inexperienced with JS.
You can see the page here. Click one of the properties, scroll to the bottom... you may have to do it a few times before you see the bug.