JWT Handler for .NET 4.5 throws error: GetIssuerName with single parameter is not supported - wif

Question

I've just implemented this JSON Web Token Handler for .Net 4.5 library described here:
http://www.cloudidentity.com/blog/2012/11/20/introducing-the-developer-preview-of-the-json-web-token-handler-for-the-microsoft-net-framework-4-5-2/
I have an ACS service that's supposed to be returning a JWT token to my application. However, at the point when I should be getting the token returned to my app (when the browser is redirected to my relying party's return uri), I instead get this exception:
WIF10200: GetIssuerName with single parameter is not supported. Call:
'GetIssuerName( SecurityToken securityToken, string issuer )'.
I don't think this is a problem directly with my code; because if I do a solution-wide search, "GetIssuerName" is not in my solution. I think it might have something to do with the certificate issuers WIF wants to trust, but I've followed the instructions in the article I linked above about importing the certificate from the ACS site's FederationMetadata... and I'm utterly stumped on this one.
Strangely enough, when I change my Relying Party token type from JWT to SAML 1 or 2, my relying party's Return Uri is never hit, I'm just redirected back to my realm error free. I would expect to finally land on my Return Uri. If someone could explain either phenomenon to me, it would help tremendously!
UPDATE
The GetIssuerName method in .NET 4.5 is part of the System.IdentityModel.Tokens.ValidatingIssuerNameRegistry class (there's also a System.IdentityModel.Tokens.ConfigurationBasedIssuerNameRegistry class with the same method, but that's not the one I'm working with).
From looking at the metadata, there are 2 overridden methods with this name in the class:
public override string GetIssuerName(SecurityToken securityToken);
public override string GetIssuerName(SecurityToken securityToken, string requestedIssuerName);
The error I'm getting from WIF seems to be coming directly from the first method listed there, as you can see from the stack trace below. With my relying party returning JWT, something somewhere is supposed to be calling the second method, whose signature has a second parameter, but is calling the first. I wish I knew how to change it.
[NotSupportedException: WIF10200: GetIssuerName with single parameter
is not supported. Call: 'GetIssuerName( SecurityToken securityToken,
string issuer )'.]
System.IdentityModel.Tokens.ValidatingIssuerNameRegistry.GetIssuerName(SecurityToken
securityToken) +156
Microsoft.IdentityModel.Tokens.JWT.JWTSecurityTokenHandler.ValidateIssuer(JWTSecurityToken
jwt, TokenValidationParameters validationParameters) +1303
Microsoft.IdentityModel.Tokens.JWT.JWTSecurityTokenHandler.ValidateToken(JWTSecurityToken
jwt, TokenValidationParameters validationParameters) +278
Microsoft.IdentityModel.Tokens.JWT.JWTSecurityTokenHandler.ValidateToken(SecurityToken
token) +2248
System.IdentityModel.Tokens.SecurityTokenHandlerCollection.ValidateToken(SecurityToken
token) +135
System.IdentityModel.Services.TokenReceiver.AuthenticateToken(SecurityToken
token, Boolean ensureBearerToken, String endpointUri) +502
System.IdentityModel.Services.WSFederationAuthenticationModule.SignInWithResponseMessage(HttpRequestBase
request) +1508
System.IdentityModel.Services.WSFederationAuthenticationModule.OnAuthenticateRequest(Object
sender, EventArgs args) +700
System.Web.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
+80 System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +165