When does Jem not react to a racial comment in To Kill a Mockingbird?

Usually, Jem reacts in anger when someone refers to his father defending Tom Robinson in a negative connotation.  These comments usually include racist phrases directed toward Tom Robinson.  Atticus experiences widespread disapproval from many people in Maycomb because of his defense of Tom Robinson.  Tom Robinson is a black man who is accused of raping a white woman.  When Mrs. Dubose speaks negatively about Atticus defending Tom Robinson, Jem becomes enraged and tears up her camellias.  He cuts off the top portion of the camellia bush with Scout's baton.
One day, Scout talks to Jem about something Cecil Jacobs had said to her.  Cecil had made a racial comment about their father defending Tom Robinson.  Instead of his typical reaction, Jem simply tells Scout to ask their father.  He is passively dismissive about the comments when Scout asks him what Cecil meant:

"Nothing," Jem said.  "Ask Atticus, he'll tell you." (To Kill a Mockingbird, Chapter 11).