If I turn on conditional comments, default ext application throw syntax error
PHP Code:
SCRIPT1004Expected ';' 
Easing.js?_dc=1350541991462line 1
SCRIPT5022
The following classes are not declared even if their files have been loaded'Ext.fx.Easing'Please check the source code of their corresponding files for possible typos'ext/src/fx/Easing.js ext-dev.js, line 9978 
PHP Code:
/*@cc_on!@*/
Ext.application({    
    
controllers: ["Main"],
    
views: ["Main"],
    
name'app',
    
autoCreateViewporttrue
}); 
It happen because first line in Easing.js look like conditional directive and IE wrong interpret it
PHP Code:
//@define Ext.fx.Easing <--- syntax error here
/** 
 * @class Ext.fx.Easing
....
 */