Whats up with Karlach and Nere?

[Simbolic]

Been wondering this for a while, not sure if anyone else noticed. That Karlach acts weird when going after Nere. She said something out the blue after a dialogue about him which made no sense. Can't remember what it was but remember before the battle with him initiating it made her Disapprove which made no sense. When he was a clearly a villain. Anyone who plays her should know she only approves when helping people or making good moral choices.
Not sure if missed something cause that made no sense at all. Unless maybe had to do with the idea of getting his Tadpole for power?

[Tingly]

The Duergar are slavers and she does not like siding with them even if it is against someone who is also a villain. You should be able to make up for it by making the duergar give up on the slaves afterwards.

[ahnenzorn]

Seems to be a bug. When you tell Nere to stop killing the slaves Karlach agrees.

In the Next step of the Conversation, you can either say that Sbou wants him dead, say that you will kill him or choose one of 2 lies. Both good and honest choices will make Karlarch disapprove, whereas lying to Nere doesn't.