UniqueConstraints Throws Veto on SaveChanges

Account.cs

using System;
using System.ComponentModel.DataAnnotations;
using Raven.Client.UniqueConstraints;

namespace UnitTests.Tests.Areas.Administration.Controllers {
  public class Account {
    public Guid Id { get; set; }
    [Required]
    [UniqueConstraint]
    public string Username { get; set; }
    [Required]
    [UniqueConstraint]
    public string Email { get; set; }
    [Required]
    public string Password { get; set; }
    [Required]
    public string FirstName { get; set; }
    [Required]
    public string LastName { get; set; }
    public DateTimeOffset Created { get; set; }
    public DateTimeOffset LastModified { get; set; }
  }
}

AccountsControllerTest.cs

using System;
using System.ComponentModel.DataAnnotations;
using Microsoft.VisualStudio.TestTools.UnitTesting;
using Raven.Client;
using Raven.Client.Document;
using Raven.Client.UniqueConstraints;

namespace UnitTests.Tests.Areas.Administration.Controllers {
  [TestClass]
  public class AccountsControllerTest {


    [TestMethod]
    public void Editing_Document_With_Unique_Constraints_SaveChanges_Vetos_Put() {
      IDocumentStore store = Initialize( "RavenDb" );
      var accountId = Guid.Empty;

      using( var session = store.OpenSession() ) {
        var account = SeedAccount();
        var check = session.CheckForUniqueConstraints( account );
        if( check.ConstraintsAreFree() ) {
          session.Store( account );
          session.SaveChanges();
          accountId = account.Id;
        }
        Assert.AreNotEqual( Guid.Empty, account.Id );
      }

      // I would think on an edit, you would not need to CheckForUniqueConstraints 
      using( var session = store.OpenSession() ) {
        var account = session.Load<Account>( accountId );
        account.FirstName = "ChangedName";
        try {
          session.SaveChanges();
          Assert.Equals( "ChangedName", account.FirstName );
        } catch( Exception ex ) {
          // We enter here due to constraint issue...
          //Assert.Fail();
          //Let's move on to test with checking for constraints first...
        }
      }

      // Just for giggles, performing a CheckForUniqueConstraints which fails obviously
      using( var session = store.OpenSession() ) {
        var account = session.Load<Account>( accountId );
        account.FirstName = "ChangedName";
        var check = session.CheckForUniqueConstraints( account );
        if( check.ConstraintsAreFree() ) {
          session.SaveChanges();
          Assert.Equals( "ChangedName", account.FirstName );
        } else {
          Assert.Inconclusive();
        }
      }
    }

    private static IDocumentStore Initialize( string connectionStringName ) {
      var instance = new DocumentStore {
        ConnectionStringName = connectionStringName
      }
      .RegisterListener( new UniqueConstraintsStoreListener() );

      instance.Conventions.TransformTypeTagNameToDocumentKeyPrefix = PreserveTypeTagNameToDocumentKeyPrefix;
      instance.Initialize();
      return instance;
    }

    private static string PreserveTypeTagNameToDocumentKeyPrefix( string typeTagName ) {
      return typeTagName;
    }

    private static Account SeedAccount() {
      var uniquePostFix = Guid.NewGuid().ToString().Replace( "-", "" );
      return new Account { Username = "User" + uniquePostFix, Email = "test" + uniquePostFix + "@test.com", FirstName = "User", LastName = "Testing", Password = "testing", Created = DateTimeOffset.Now, LastModified = DateTimeOffset.Now };
    }
  }
}