The fire method in Ext.util.Event adds an additional object to the event arguments. Is this intended or a bug?

Example:
Code:
new Ext.Button({
    text:'Hello World',
    renderTo:Ext.getBody(),
    listeners:{
        click:function(){
                console.log(arguments);
        }
    }
});
In Ext3 you get 2 arguments:
Code:
 [Object { initialConfig={...},  text="Hello World",  more...}, Object { browserEvent=,  button=0,  more...}]
In Ext4 you get 3 arguments:
Code:
 [Object { initialConfig={...},  text="Hello World",  more...}, Object { browserEvent=,  type="click",  more...}, Object {}]
This is caused by ext-core-debug.js:12813:fire:
Code:
                        if (listener.o) {
                            args.push(listener.o);
                        }