title: Unhandled Exception after Upgrading to Entity Framework 4.3.1
body: <p><strong>Error:</strong> </p>
  
  <p>Unhandled Exception: System.Data.SqlClient.SqlException: The operation failed because an index or statistics with name 'IX_ID' already exists on table 'PrivateMakeUpLessons'.</p>
  
  <p><strong>Model (Simplified, building in a separate test project for debugging):</strong> </p>
  
  <pre><code>public abstract class Lesson
  {
      public Guid ID { get; set; }
      public string Room { get; set; }
      public TimeSpan Time { get; set; }
      public int Duration { get; set; }
  }
  
  public abstract class RecurringLesson : Lesson
  {
      public int DayOfWeek { get; set; }
      public DateTime StartDate { get; set; }
      public DateTime EndDate { get; set; }
      public string Frequency { get; set; }
  }
  
  public class PrivateLesson : RecurringLesson
  {
      public string Student { get; set; }
      public string Teacher { get; set; }
      public virtual ICollection&lt;Cancellation&gt; Cancellations { get; set; }
  }
  
  public class Cancellation
  {
      public Guid ID { get; set; }
      public DateTime Date { get; set; }
      public virtual PrivateLesson Lesson { get; set; }
      public virtual MakeUpLesson MakeUpLesson { get; set; }
  }
  
  public class MakeUpLesson : Lesson
  {
      public DateTime Date { get; set; }
      public string Teacher { get; set; }
      public virtual Cancellation Cancellation { get; set; }
  }
  </code></pre>
  
  <p><strong>Configuration:</strong></p>
  
  <pre><code>protected override void OnModelCreating(DbModelBuilder modelBuilder)
  {
      modelBuilder.Entity&lt;Lesson&gt;().ToTable("Lessons");
      modelBuilder.Entity&lt;RecurringLesson&gt;().ToTable("RecurringLessons");
      modelBuilder.Entity&lt;PrivateLesson&gt;().ToTable("PrivateLessons");
      modelBuilder.Entity&lt;MakeUpLesson&gt;().ToTable("PrivateMakeUpLessons");
  
      modelBuilder.Entity&lt;Cancellation&gt;()
          .HasOptional(x =&gt; x.MakeUpLesson)
          .WithRequired(x =&gt; x.Cancellation);
  
      base.OnModelCreating(modelBuilder);
  }
  </code></pre>
  
  <p><strong>Notes</strong>: </p>
  
  <p>This worked fine in EF 4.2. Is there something wrong with my model? The actual model is much more complicated which is why I have all the classes abstracted out. Also, I am working against an existing database so I need to use Table-Per-Type inheritance.</p>
  
  <p>If I change the relationship of <code>Cancellation</code> to <code>PrivateMakeUpLesson</code> from 1 to 0..1 to 0..1 to 0..1 it works. This is undesirable because you can't have a <code>PrivateMakeUpLesson</code> without a <code>Cancellation</code>.</p>
  
  <p>Also, if I make <code>PrivateMakeUpLesson</code> NOT inherit from <code>Lesson</code> then it also works, but it IS a lesson and needs to remain so for existing business logic.</p>
  
  <p>I'd appreciate any guidance. Thank you!</p>
  
  <p><strong>Edit</strong>:</p>
  
  <p>Starting a bounty. I can't find any documentation on what changed between EF 4.2 and EF 4.3 with regard to the index generation for code first. It's clear that EF 4.3 is creating more indexes and that the naming scheme has changed but I want to know if there's a bug in EF or if there is something fundamentally wrong with my model or fluent API configuration.</p>