title: Material skin gone when i use ismdicontainer
body: <p>I have one form with IsMdiContainer = True and when I run the form material skin disappears.</p>
  <p><a href="https://i.stack.imgur.com/92z9H.png" rel="nofollow noreferrer">Form</a></p>
  <p>below is when I run the form material skin just disappear.</p>
  <p><a href="https://i.stack.imgur.com/1PJfD.png" rel="nofollow noreferrer">Material Skin Gone</a></p>
  <p>Form Code</p>
  <pre><code> MaterialSkinManager materialSkinManager = MaterialSkinManager.Instance;
          materialSkinManager.AddFormToManage(this);
          materialSkinManager.Theme = MaterialSkinManager.Themes.LIGHT;
  
          // Configure color schema
          materialSkinManager.ColorScheme = new ColorScheme(
              Primary.Blue400, Primary.Blue500,
              Primary.Blue500, Accent.LightBlue200,
              TextShade.WHITE
          );
  </code></pre>
  <p>in the form i have ShowForm</p>
  <pre><code> private void ShowForm(Form f)
      {
          f.MdiParent = this;
          f.Show();
          f.Activate();
      }
  </code></pre>