Right-sidebar ends up on bottom?

I’ve noticed that, browsing through a few templates from teh themeviewer here and other sites, sometimes I come across a theme where the right-hand sidebar is shoved at the bottom of the page, under all of the posts. This is also the case on my website.

Any ideas as to what causes it?
I’m using IE – I mention this because I get the feeling that it’s got something to do with it.

Anyone else noticed this, even browsing through some of the www.remarpro.com templates (when using the Test Run option)?