Using command attribute in child classes

Let's assume I have following classes:

 public abstract class BaseClass : NetworkBehaviour{
     public abstract void CmdMakeAction();
 }

 public class Derived : BaseClass {
     [Command]
     public override void CmdMakeAction() {
         if (!isServer) {
             Debug.Log("WRONG! Executing CmdMakeAction on client!");
         }
     }
 }

The problem is that it looks like unity is executing CmdMakeAction not only on server, but on clients too.

However, if I remove CmdMakeAction from abstract class and remove "override" keyword from Derived, then things begin to work.

Is this my error somewhere [I am coding almost 16 hours =( ] or is it well-known behavior?

P.S. Unity version is 5.6.0f3