Ext.util.Cookies.set uses path "/" by default.
Ext.util.Cookies.clear doesn't set a path so it doesn't remove a session cookie.

This override fixes this issue:
Code:
Ext.util.Cookies.clear = function(name) {    
   if(Ext.util.Cookies.get(name)){
        document.cookie = name + "=" + "; expires=Thu, 01-Jan-70 00:00:01 GMT; path=/";
    }
};
99% of the times people will use the path "/" for cookies anyway.

There are several reports about this issue but the team choose to ignore them:
http://www.sencha.com/forum/showthre...t=cookie+clear
http://www.sencha.com/forum/showthre...560#post462560
http://www.sencha.com/forum/showthre...-does-not-work
http://www.sencha.com/forum/showthre...ear-is-Invalid
http://jupiter.mcom.fr/~clucas/blog/...clear-a-cookie