Nyki's point is valid, and probably correct, but given the way they have tended to gloss over these things with companions it wasn't something that I immediately thought of as a reason for his short temper. Just look at other examples. Nyssa is a good one. Her entire world was destroyed and a madman is running around in her fathers body and yet within days she was laughing and joking with Adric. Sometimes they just tend to forget what happened previously.
That's true, but I'd say the character continuity was a lot better early on (as it is on NuWho) perhaps partly because the show was on almost continuously. Although a lot of good things came out of the JNT era, continuity wasn't a noticeable one.