Continuity mistake: Shortly after halfway through the episode, Carrie Matthews discusses the fate of her unborn child with her sister and father. Her hair is not tucked behind her ears - then it quickly is.
Continuity mistake: When Carrie is talking to Brody from across the room, her hair jumps several times between being tucked behind her ear to hanging down by her face. (00:20:30)
Chosen answer: Everyone else calls him Brody or Sgt. Brody, and it probably became habit to her.
The_Iceman
Can't get the source but I read that even the Producer responded to that. Stating that it was common practise for a military wife living in a military complex as everybody refers to their husband by their last name.