The problem is with IE.
IE decided that intranet sites are best viewed when compatibility mode is on - so whenever IE identifies an internal web site it turns on compatibility mode (yes I know it's evil)...
You can use X-UA-Compatible in two ways...
1. Add to web.config
<configuration>
<system.webserver>
<httpprotocol>
<customheaders>
<clear />
<add name="X-UA-Compatible" value="edge" />
</customheaders>
</httpprotocol>
</system.webserver>
</configuration>
2. Add to page (in which case it must be the first meta-line)
<html>
<head>
<meta http-equiv="x-ua-compatible" content="edge">
</meta></head>
</html>
The other option is to turn of IE behavior from the menu Tools->Compatibility View Settings...