AddOutValue/LoadProperty not functioning on Guid data type in Business Rule

I have been scratching my head for some time trying to figure out why my business rule wasn't setting a Guid property on my business object, since I had done this sort of thing before. However, it occurred to me that the other properties I was setting were strings and primitive values.

So, I copied and pasted my UserId property (a guid) and made it into a string. Then I wired up the new property to my business rule, and it works. The thing is, I need it to be a Guid.

I tried both the AddOutValue and LoadProperty techniques to set the output of my rule, but it doesn't function with Guid in either case. So is there something special I have to do to make this work, or did I find a bug?

Here are my properties (Identical in every way except datatype):

        public static readonly PropertyInfo<Guid> UserIdProperty = RegisterProperty<Guid>(c => c.UserId);
        public Guid UserId
        {
            get { return GetProperty(UserIdProperty); }
            private set { LoadProperty(UserIdProperty, value); }
        }

        public static readonly PropertyInfo<string> UserIdStringProperty = RegisterProperty<string>(c => c.UserIdString);
        public string UserIdString
        {
            get { return GetProperty(UserIdStringProperty); }
            private set { LoadProperty(UserIdStringProperty, value); }
        }

And this is my business rule:

    public class UserHasConfirmedAccountRule
        : PropertyRule
    {
        public UserHasConfirmedAccountRule(
            Type modelType,
            ILocalizedStringProvider localizedStringProvider,
            IPropertyInfo emailAddressOrPublicNameProperty,
            IPropertyInfo tenantIdProperty,
            IPropertyInfo userIdProperty,
            IUserAccountRepository userAccountRepository
            )
            : base(emailAddressOrPublicNameProperty, modelType, localizedStringProvider)
        {
            if (emailAddressOrPublicNameProperty == null)
                throw new ArgumentNullException("emailAddressOrPublicNameProperty");
            if (tenantIdProperty == null)
                throw new ArgumentNullException("tenantIdProperty");
            if (userIdProperty == null)
                throw new ArgumentNullException("userIdProperty");
            if (userAccountRepository == null)
                throw new ArgumentNullException("userAccountRepository");

            this.emailAddressOrPublicNameProperty = emailAddressOrPublicNameProperty;
            this.tenantIdProperty = tenantIdProperty;
            this.userIdProperty = userIdProperty;
            this.userAccountRepository = userAccountRepository;

            InputProperties = new List<IPropertyInfo> { emailAddressOrPublicNameProperty, tenantIdProperty, userIdProperty };
            AffectedProperties.Add(userIdProperty);
        }

        private readonly IPropertyInfo emailAddressOrPublicNameProperty;
        private readonly IPropertyInfo tenantIdProperty;
        private readonly IPropertyInfo userIdProperty;
        private readonly IUserAccountRepository userAccountRepository;

        protected override void Execute(CslaLibrary.Rules.RuleContext context)
        {
            var emailAddressOrPublicName = (string)context.InputPropertyValues[emailAddressOrPublicNameProperty];
            var tenantId = (int)context.InputPropertyValues[tenantIdProperty];

            bool exists = false;
            Guid userId = Guid.Empty;
            if (!string.IsNullOrEmpty(emailAddressOrPublicName) && tenantId > 0)
            {
                userId = userAccountRepository.HasConfirmedAccount(tenantId, emailAddressOrPublicName);
                if (userId != null && !userId.Equals(Guid.Empty))
                {
                    exists = true;
                    context.AddOutValue(userIdProperty, userId.ToString());

                    //var target = (ResetPassword)context.Target;
                    //LoadProperty(target, userIdProperty, userId.ToString());
                }
            }

            if (!exists)
                context.AddErrorResult(GetMessage());
        }
    }

Note that I am using a subclass of PropertyRule, but I changed it to the CSLA BusinessRule type and still got the same result. Also note the code above is the version that works - I wouldn't use .ToString() when trying to set a guid.