EF4.1 Hierarchy-based database creation exception

I created a very simple project to demonstrate hierarchy inheritance. In my unit test, which is trying to generate a database, I get one of several errors depending on the configuration:

no method Required()

Map<InActiveUser>(x => x.Requires("IsActive").HasValue(false));
Map<ActiveUser>(x => x.Requires("IsActive").HasValue(true));

provides:

System.Data.DataException : An exception occurred while initializing the database. See the InnerException for details.
  ----> System.Data.EntityCommandCompilationException : An error occurred while preparing the command definition. See the inner exception for details.
  ----> System.Data.MappingException : 
(6,10) : error 3032: Problem in mapping fragments starting at line 6:Condition member 'User.IsActive' with a condition other than 'IsNull=False' is mapped. Either remove the condition on User.IsActive or remove it from the mapping.

using the method Required():

Map<InActiveUser>(x => x.Requires("IsActive").HasValue(false).IsRequired());

Map<ActiveUser>(x => x.Requires("IsActive").HasValue(true).IsRequired());

provides:

System.Data.DataException : An exception occurred while initializing the database. See the InnerException for details.
  ----> System.Data.EntityCommandCompilationException : An error occurred while preparing the command definition. See the inner exception for details.
  ----> System.Data.MappingException : 
(6,10) : error 3023: Problem in mapping fragments starting at lines 6, 13, 19:Column User.IsActive has no default value and is not nullable. A column value is required to store entity data.

From what I understand, we should not define the column / property of the discriminator in the base type, but in any case, it does not make any difference with or without the definition of the column:

  public class User
  {
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public virtual int Id { get; set; }

    [Required]
    public virtual string Username { get; set; }

    [Required]
    [DefaultValue(true)]
    public bool IsActive { get; set; } //have tried without this property
  }

  public class InActiveUser : User
  {
    public virtual DateTime DeActivatedDate { get; set; }
  }

  public class ActiveUser : User
  {
  }