asp.net mvc 3服务器端远程验证不通过fiddler提交。

I am trying to understand how remote validation works. It works great client side or in browser. This is what I did, I need to check if a username exists while registration. So I added remote validation and it worked perfectly in browser. I wanted to test it on submit, so I captured the request in Fiddler and changed the username to something that exists and then submitted the request. It accepted. RemoteValidation did not occur (of course it failed at db). Hence doesn't it validate on server side?I am trying to understand how remote validation