title: IsMemberOf() returns false incorrectly
body: <p>I'm am creating an ASP.net intranet site and I'm trying to get group membership.  I have the following code:</p>
  
  <pre class="lang-cs prettyprint-override"><code>PrincipalContext cntxt = new PrincipalContext(ContextType.Domain);
  GroupPrincipal adminGroup = new GroupPrincipal(cntxt, "Help");
  UserPrincipal user = UserPrincipal.FindByIdentity(cntxt, "domainuser");
  
  var boolvalue =user.IsMemberOf(adminGroup);
  </code></pre>
  
  <p>boolvalue is returning as false.</p>
  
  <p>If I debug with:</p>
  
  <pre class="lang-cs prettyprint-override"><code>var foo = User.GetGroups();
  </code></pre>
  
  <p>I get a list of all the groups that the user is a member of.</p>
  
  <p>but </p>
  
  <pre class="lang-cs prettyprint-override"><code>var bar = adminGroup.GetMembers();
  </code></pre>
  
  <p>shows that it can't seem to get the group from AD as all the members are null.</p>
  
  <p>I've tried using </p>
  
  <pre class="lang-cs prettyprint-override"><code>PrincipalContext cntxt =new PrincipalContext(ContextType.Domain, "ADdomain.local");
  </code></pre>
  
  <p>but that didn't fix the issue.</p>
  
  <p>I'm not getting any build or syntax errors either.</p>