at first here is my code:
PrincipalContext ctx = new PrincipalContext(ContextType.Domain, "Domain");
GroupPrincipal gpx = GroupPrincipal.FindByIdentity(ctx, IdentityType.Name, "otheradmingroup");
List<string> Members = new List<string>();
foreach(Principal member in gpx.GetMembers(true))
the only member of my "otheradmingroup" is the "Domain Admins" group, which contains 6 ad-users.
after executing this code above, the returned list contains only the first 4 members of my "Domain Admins"
I've found the Problem.
The GetMembers() Method don't find users which have this group as there primary group.