IE9 (also IE8),by default, display intranet sites in compatibility mode. As result, state of the art sites might not display correctly (depending how they are accessed).
One of my recently deployed web applications, built with Telerik controls, did not look exactly the same way in staging as it did in development. The client was not happy about a few scrollbars appearing for no evident reason and some images showing in plainly wrong spots. I did not blame the client I did not like the staging site look either.
The page source rendered by a development machine and by a staging server looked the same. Checking for any failing requests in Fiddler brought nothing. After some more troubleshooting I found few leads (blank lines in front of DOCTYPE directive, ASCII vs. UTF file encoding issue) but none solved the problem. At some point, I noticed that IE compatibility mode is turned on for the staging site but off for the development site. And finally I stumbled on a IE related blog post on Microsoft site explaining it all.
IE makes assumption about displaying intranet sites (http://someInternalSite/ vs. http://someInternalSite.myCompany.org). That assumption is that intranet sites work best in compatibility mode. To fix it either access the site with FQDN or uncheck a checkbox in “Compatibility View Settings”: