Posted on May 20, 2011 | Magento 1
If you experience compatibility problems try turning on compatibility mode in IE9 by clicking the small compatibility button in the address bar. If this resolves the problem you can implement the compatibility META tag by editing the head.phtml file of your themes template e.g. app/design/frontend/YOURTHEME/default/template/page/html/head.phtml in older Magento versions.
My Issue: When adding a product and clicking "Categories" or any tab below this, a blank screen is produced and the css is stripped.
My Fix:
Firstly open the admin head.phtml file within app/design/adminhtml/YOURTHEME/default/template/page/head.phtml.
The following Meta TAG should be placed directly above the < title > tag:
I found the above Meta Tag wasnt enough to solve my issue so I also added the following to the .htaccess file which forced IE9 to be compatible.
BrowserMatch MSIE best-standards-support Header set X-UA-Compatible IE=8 env=best-standards-support
With these two snippets in place, it solved my issue.
Hope this helps.