ASP.NET TableStorageProvider for Azure tables not persisting users ?

Question

I have a windows azure Webrole application using Silverlight on top of WCF+ASP.NET. I found this useful ASP.NET provider for Azure tables in the Azure samples and implemented it. I authenticate my users with the WCF service System.Web.ApplicationServices.AuthenticationService.

It works great: I create my users with a very simple ASP.NET form, then I go to my Silverlight app and authenticate successfully, but when I shutdown the Azure development storage environment and restart it, I can't log in again, even if the user is still in the Membership table. I debugged the logging process and found that when the provider executes the query to the table, it throw an exception in this method:

private MembershipRow GetUserFromTable(DataServiceContext svc, string username)
    {
        SecUtility.CheckParameter(ref username, true, true, true, Constants.MaxTableUsernameLength, "username");

        DataServiceQuery<MembershipRow> queryObj = svc.CreateQuery<MembershipRow>(_tableName);

        var query = (from user in queryObj
                     where user.PartitionKey == SecUtility.CombineToKey(_applicationName, username) &&
                           user.ProfileIsCreatedByProfileProvider == false
                     select user).AsTableServiceQuery();

        IEnumerable<MembershipRow> allUsers = query.Execute();
        if (allUsers == null)
        {
            return null;
        }
        IEnumerator<MembershipRow> e = allUsers.GetEnumerator();
        if (e == null)
        {
            return null;
        }
        // e.Reset() throws a not implemented exception
        // according to the spec, the enumerator is at the beginning of the collections after a call to GetEnumerator()
        if (!e.MoveNext())
        {
            return null;
        }
        MembershipRow ret = e.Current;
        if (e.MoveNext())
        {
            throw new ProviderException("Duplicate elements for primary keys application and user name.");
        }
        return ret;
    }

the queryObj variable contains the user entry when I check during execution, but query looks like it contains an exception in one of its member. Finally, the execution fails when making the e.moveNext().

If I just delete all the Membership tables and blobs and recreate a user, it works just normally.