Syntactically invalid request submitted when submitting form with invalid data in Spring MVC (which uses Hibernate Validator)

Login form:

<f:form class="form-horizontal" method="post" action="/login"
    commandName="logindata">
    <fieldset>
        <legend class="text-info">Login</legend>
        <div class="control-group">
            <f:label path="uname" class="control-label" for="uname">Username</f:label>
            <div class="controls">
                <f:input type="text" path="uname" name="uname" id="uname"
                    placeholder="Username" />
            </div>
        </div>
        <div class="control-group">
            <f:label path="pwd" class="control-label" for="pwd">Password</f:label>
            <div class="controls">
                <f:input type="password" path="pwd" name="pwd" id="pwd"
                    placeholder="Password" />
            </div>
        </div>
        <div class="control-group">
            <div class="controls">
                <button type="submit" class="btn" id="login">
                    Login <i class="icon-chevron-right"></i>
                </button>
            </div>
        </div>
        <div id="errormsg" class="alert alert-error">${message}</div>
    </fieldset>
</f:form>

class loginData:

package com.demo.forms;

import org.hibernate.validator.constraints.Length;
import org.hibernate.validator.constraints.NotEmpty;

public class loginData {
    @Length(min=4)
    private String uname; 

    @NotEmpty
    private String pwd;

    public String getUname() {
        return uname;
    }
    public void setUname(String uname) {
        this.uname = uname;
    }
    public String getPwd() {
        return pwd;
    }
    public void setPwd(String pwd) {
        this.pwd = pwd;
    }
}

Controller methods for showing and submitting the form: (shows the home page containing the registration form and the login form)

@RequestMapping(value = "/", method=RequestMethod.GET)
    public String showHome(Model model)
    {
        loginservice.logout();
        model.addAttribute("logindata", new loginData());
        model.addAttribute("signupdata", new signupData());
        return "home";
    }

The method caused the login form to be submitted:

@RequestMapping(value = "login", method=RequestMethod.POST)
    public String submitloginForm(@Valid loginData logindata, SessionStatus state, Model model, BindingResult result)
    {
            if((loginservice.loggedin()) || (result.hasErrors()))
            {
                return showHome(model);
            }
            else
            {
                String uname = logindata.getUname();
                String pwd = logindata.getPwd();
                if(loginservice.login(uname, pwd))
                {
                    model.addAttribute("user",uname);
                    return "redirect:profile";
                }
                else
                {
                    model.addAttribute("message","Invalid Username/Password");
                    return showHome(model);
                }   
            }   
    }

Logging in works fine when the data entered is "valid" (correct or incorrect). However, if this is not valid, for example, when the password field is empty or the username is less than four characters, the following error is displayed:

The request sent by the client was syntactically incorrect.

Any idea how this could be fixed?