title: HttpRequest.Content.IsMimeMultipartContent() is returning false when it should return true
body: <p>I need to send an HTTP request as a MultiPartFormData to a REST controller. It was working, but now the check I have on my controller is claiming that the request is not of the correct type, even when I can see in the debugger that the request is on the correct type. For reference:</p>
  
  <p><a href="https://i.stack.imgur.com/DrYJk.png" rel="noreferrer"><img src="https://i.stack.imgur.com/DrYJk.png" alt="enter image description here"></a></p>
  
  <p>Here's the console app code that is calling it:</p>
  
  <pre><code>using System;
  using System.IO;
  using System.Net.Http;
  using System.Net.Http.Headers;
  using System.Text;
  
  namespace QuickUploadTestHarness
  {
      class Program
      {
          static void Main(string[] args)
          {
              using (var client = new HttpClient())
              using (var content = new MultipartFormDataContent())
              {
                  // Make sure to change API address
                  client.BaseAddress = new Uri("http://localhost");
  
                  // Add first file content 
                  var fileContent1 = new ByteArrayContent(File.ReadAllBytes(@"C:\&lt;filepath&gt;\test.txt"));
                  fileContent1.Headers.ContentDisposition = new ContentDispositionHeaderValue("attachment")
                  {
                      FileName = "testData.txt"
                  };
  
                  //Add Second file content
                  var fileContent2 = new ByteArrayContent(File.ReadAllBytes(@"C:\&lt;filepath&gt;\test.txt"));
                  fileContent2.Headers.ContentDisposition = new ContentDispositionHeaderValue("attachment")
                  {
                      FileName = "Sample.txt"
                  };
  
                  content.Add(fileContent1);
                  content.Add(fileContent2);
  
                  // Make a call to Web API
                  var result = client.PostAsync("/secret/endpoint/relevant/bits/here/", content).Result;
  
                  Console.WriteLine(result.StatusCode);
                  Console.ReadLine();
              }
          }
      }
  }
  </code></pre>
  
  <p>How is it possible that it's being interpreted as not MultiPartFormData?     Note the "<strong>using MultiPartFormDataContent</strong>" for the request</p>