"compatibility mode" is an IE browser feature. It effectively mean "pretend to be IE7". We do not support IE7 any longer. IE will go into compatibility mode automatically if it detects that you are using an intranet.
1. make sure your have the "unsupported browser" feature enabled in template manager
2. you can also try putting this line in the head section of your templates index.php file (remember that it will get overwritten by templates upgrades though)
<meta http-equiv="X-UA-Compatible" content="IE=Edge" />
Regards, Mark.