1. While playing a DiD* character I had Lydia as a follower. On a mission for the Companions to take out a Silverhand group we took out all the exterior bad guys and had only the boss left to kill, who was sitting by himself at the top of a tower of a derelict fort. Now, during the battle on the outside of the fort, Lydia kept running off as if she'd seen another Silverhand; but there weren't any. At one point she ran over the hill behind the fort and found a couple of wolves, who otherwise wouldn't have been part of the action.

At any rate, I went and got her and brought her back to the fort with me. She followed me into a doorway and then disappeared. I walked back out of the door and she wasn't there. So I walked out of the fort and down the road and waited for an hour. She still wasn't there. Then I waited for two more hours and she appeared. So I went back in to the fort and up the stairs in the tower and attacked the boss, thinking she was behind me. But she wasn't and my character was killed. What happened?

2. Do different Housecarls have different quirks? For example, I figured that all the Housecarls were essentially the same character with only superficial looks and voice qualities. Otherwise they all fight and follow the same way: heavy armor, one handed attack, archery, etc. But the quirkiest things happen with Lydia. For example in Xbox you're supposed to be able to marry her but you can't; and she's the only one with a sour attitude about trading things with you. What I'm wondering is if maybe she's prone to to bail on you if something else catches her attention or if this was an anomaly. Also, while all followers can get in your way during a battle, she seems to be the worst. In addition, both Jordis and Iona seem to be more effective fighters under all circumstances. I've only gotten Iona killed once and Jordis never.

*DiD means Dead is Dead; meaning that you don't reload the game and try again. Once the character dies, you never play it again; even if it dies in Helgen jumping out of the tower. You have to start all over.

Your followers leave during a lot of the companions quests because for most missions you get another follower to replace. Vilkas, Aela, etc, and you can only have one at a time. As far as running off to fight wolves, that's just bad AI.

And the housecarls are all exactly the same when it comes skills and stats.

Mjoll has a habbit of doing this with me but i noticed it moreso with Companions quests. She either goes off hunting, just vanishes into thin air, starts fights with Shadowmere or gets over eager and kills the hostage were sent to rescue.
I never use the Companions as followers after Vilkas proved to be an utter wet wipe on one of the Silver Hand missions by spending more time on his knees than on his feet.

Did you try a different deodorant?