Why does Matt refuse to enter Kira's room in Gathering Blue?

Although Matt is only eight or nine years old, and although he displays a lack of manners consistent with his upbringing in the Fen, he declines to enter Kira's room with her when Jamison ushers them down the corridor. Matt and his dog, Branch, have been allowed by Jamison to enter the Council Edifice because Kira needs his assistance with carrying her personal possessions. When Jamison and Kira enter her room, Matt stops in the hall of his own accord. By way of explanation, he declares, "Me and Branch, we don't go into the room because of the wee buggies." Kira at first thinks he means the beetle Branch was eating, but she realizes it was already consumed and that it couldn't have been described as "wee." Jamison asks Matt what he means, and he clarifies, "Branch got fleas." Jamison shakes his head and thinks it's slightly funny. On a later occasion, when Kira and Thomas prevent Matt from going on the hunt, Thomas scrubs Matt and Branch clean in his bathroom tub.