So, i have 2 forms, one is for sign up, and another is for sign in

<div class="row">
<div class="col-md-6">
    <h3>Sign Up</h3>
    <form action="{{ route('signup') }}" method="post">
        <div class="form-group">
            <label for="email">Your E-Mail</label>
            <input class="form-control" type="email" name="su_email" id="email">
        </div>
        <div class="form-group">
            <label for="first_name">First Name</label>
            <input class="form-control" type="text" name="first_name" id="first_name">
        </div>
        <div class="form-group">
            <label for="password">Password</label>
            <input class="form-control" type="password" name="su_password" id="password">
        </div>
        {{ csrf_field() }}
        <button class="btn btn-primary">Submit</button>
    </form>
</div>
<div class="col-md-6">
    <h3>Sign In</h3>
    <form action="{{ route('signin') }}" method="post">
        <div class="form-group">
            <label for="email">Your E-Mail</label>
            <input class="form-control" type="email" name="si_email" id="email">
        </div>
        <div class="form-group">
            <label for="password">Password</label>
            <input class="form-control" type="password" name="si_password" id="password">
        </div>
        {{ csrf_field() }}
        <button class="btn btn-primary">Submit</button>
    </form>
</div>

Here is my controller

public function postSignUp(Request $request)
{
    $email = $request['su_email'];
    $first_name = $request['first_name'];
    $password = bcrypt($request['su_password']);

    $user = new User();
    $user->email = $email;
    $user->first_name = $first_name;
    $user->password = $password;
    $user->save();
    return redirect()->back();
}
public function postSignIn(Request $request)
{
    if (Auth::attempt(['email' => $request['si_email'], 'password' => $request['si_password']])) {
        return view('dashboard');
    }
    return redirect()->back();
}

So the problem is: when i enter values in "sign in" form, and then go back to page, in my "first_name" field i have "si_email" value, and in "su_password" i have "si_password" value

Why this happens? I didnt set any value in my html.