title: Linq when using GroupBy, Include is not working
body: <p>include matchparticipants is not working. It always says Null when I debug.
  But when I put the GroupBy in comment it works fine. I am using Entity framework 4.3.1 with code-first.</p>
  
  <p>Entities:</p>
  
  <pre><code>public class Match
      {
          [ScaffoldColumn(false)]
          public int MatchId { get; set; }
  
          [Required(ErrorMessage = "Matchtype is a required field")]
          public int Scheme { get; set; }
  
          [Required]
          [DefaultValue(false)]
          public bool Finished { get; set; }
  
          public int Round { get; set; }
  
  
          // Relations
          [Required]
          public Category Category { get; set; }
  
          public Official Official { get; set; }
  
          public Slot Slot { get; set; }
  
          public ICollection&lt;MatchParticipant&gt; MatchParticipants { get; set; }
      }
  
   public class MatchParticipant
      {
          [ScaffoldColumn(false)]
          public int MatchParticipantId { get; set; }
  
          public int Points { get; set; }
  
          public int Goals { get; set; }
  
          [Required]
          public Match Match { get; set; }
  
          [Required]
          public Team Team { get; set; }
      }
  
  public class Team
      {
          [ScaffoldColumn(false)]
          public int TeamId { get; set; }
  
          [Required(ErrorMessage="Name is a required field")]
          public string Name { get; set; }
  
          [Required(ErrorMessage="Number of players is a required field")]
          public int NumberOfPlayers { get; set; }
  
          [Required(ErrorMessage="Coach is a required field")]
          public string Coach { get; set; }
  
          [Required(ErrorMessage="Phone is a required field")]
          public string Phone { get; set; }
  
          public string CellPhone { get; set; }
  
          public string Fax { get; set; }
  
          [Required(ErrorMessage="Email is a required field")]
          public string Email { get; set; }
  
          [Required(ErrorMessage="Address is a required field")]
          public Address Address { get; set; }
  
          public Pool Pool { get; set; }
  
          [Required(ErrorMessage = "Category is a required field")]
          public Category Category { get; set; }
  
          public ICollection&lt;MatchParticipant&gt; matchParticipants { get; set; }
      }
  
          var matches =
          context.matches
         .Include("Official")
         .Include("Slot")
         .Include("MatchParticipants.Team")
         .Include("Category.Tournament")
         .Where(m =&gt; m.Category.Tournament.TournamentId == tournamentId)
         .GroupBy(m =&gt; m.Category);
  </code></pre>
  
  <p>How can I make the Include work?</p>