Logging In To Website Opens A New Tab?

I've been working on my personal website as of late, and even thought it's not a big problem because I'm the only one that sees it, it's annoying nonetheless.

Whenever I go to my login page, it all works fine. If I enter a bad username/password, it will just print a simple text message error(intended). But, if I login correctly, then instead of redirecting to the root of my website as I intend, it will instead create a new tab in firefox and from there it will be in / (which is correct). The problem is why does it create a new tab? I didn't even think forms were capable of such a thing:

My full login page is at [URL] The gist of it is:

<form method="post" target="/login">
Username: <input type="text" name="username" /> <br />
Password: <input type="password" name="password" /> <br />
<input type="submit" name="Submit" />
</form>

And my server side code is also very simple:

if(RouteID=="login"){
if(AuthenticationModule.Login(Form["username"],Form["password"],false)){
//logged in correctly
Response.Redirect("/"); //just go to the root of my site
}else{
Write("You fail at life");
}
}