So your using HTML 5 now. You just put in your DOCTYPE as:

You open up your HTML 5 page in IE9 to discover that it forces you automatically into IE9 Compatibility view! WHAT? Why would I want to be in compatibility mode when I’m building a new website?

The key is that in the specifications you cannot have anything render before the DOCTYPE. So simply remove any comments you may have put in above the DOCTYPE and you’ll notice everything is now working as expected! Makes sense….but very disappointing if you lost some time to something so inconspicuous.