I just completed a new web design project using WordPress and HTML5. I did my normal browser testing with IE7, IE8, IE9, FireFox, Chrome, and Safari.
Everything looked good and I uploaded all the files to the server.
The following day my client told me there was an issue on their end with IE9, but all other browsers look fine.
They sent me this screen shot of how the website look like with IE9.
The funny part was that I did not see the same errors on my IE9.
Then I found the solution and it was very simple.
Add the following META tag and paste it between the HTML header tags.
IE9 rendering solution with HTML5
<meta http-equiv="X-UA-Compatible" content="IE=EmulateIE8" >
This fixed the problem with IE9, I’m not exactly sure what happened, but you if come across similar situation, just remember to add this meta tag.