title: Update-Database fails due to Pending Changes, but Add-Migration Creates a Duplicate Migration
body: <p>I'm working with Entity Framework 5.0 Code First Migrations, and am having a problem with running Update-Database. It says there are pending model changes; but it should be up-to-date, so I run</p>
  
  <pre><code>Add-Migration SomeMigrationName
  </code></pre>
  
  <p>and it creates a file... however, it creates a file which is essentially the same a duplicate of a prior Migration (if I try to Update-Database again on that file, it fails with issues related to trying to drop a non-existent constraint).  Furthermore, I have been able to confirm that the 'original' migration has been run based on both the data model in the DB, and from the presence of a record in the __MigrationHistory table!</p>
  
  <p>If I delete the whole database, and run all the migrations again, automatically or by hand, I have the same problem.</p>
  
  <p>The 'original' migration file I had is as follows:</p>
  
  <pre><code>public partial class RenameLinkColumns : DbMigration
  {
      public override void Up()
      {
          DropForeignKey("dbo.Listing", "OfferedByUserId", "dbo.User");
          DropIndex("dbo.Listing", new[] { "OfferedByUserId" });
          AddColumn("dbo.Listing", "ListedByUserId", c =&gt; c.Int(nullable: false));
          AddForeignKey("dbo.Listing", "ListedByUserId", "dbo.User", "UserId", cascadeDelete: true);
          CreateIndex("dbo.Listing", "ListedByUserId");
          DropColumn("dbo.Listing", "OfferedByUserId");
      }
  
      public override void Down()
      {
          AddColumn("dbo.Listing", "OfferedByUserId", c =&gt; c.Int(nullable: false));
          DropIndex("dbo.Listing", new[] { "ListedByUserId" });
          DropForeignKey("dbo.Listing", "ListedByUserId", "dbo.User");
          DropColumn("dbo.Listing", "ListedByUserId");
          CreateIndex("dbo.Listing", "OfferedByUserId");
          AddForeignKey("dbo.Listing", "OfferedByUserId", "dbo.User", "UserId", cascadeDelete: true);
      }
  }
  </code></pre>
  
  <p>When I ran that Add-Migration again, the Up/Down methods in that file are exactly the same as these.</p>
  
  <p>I'm quite impressed that migrations were correctly able to detect that I had renamed a ForeignKey column; but is that what is causing this to choke?</p>
  
  <p>It seems there is a work-around: I have deleted the database, and all migration files, and created a new 'Initial' Migration, but I would prefer not to do this if possible.</p>
  
  <p><strong>Update:</strong> This was <em>not</em> the latest migration that caused this issue, but the problem started after a merge (I am working alone, but am simulating team work on branches to learn more about git too), and trying to get the database in step with the  merge. Might this have come about from placing migrations in some particular order after a merge - though a noted, the migrations <em>did</em> work as expected in the order they ran when I gave them an empty DB.</p>
  
  <p>Additionally, this original migration needed manually tweaking when the tables had data in, because data needed to be copied from the old to the new column. However, I tested that file with and without my manual edits in that file, and still encountered the behaviour noted.</p>