So, after you choose one of the 3 options concerning the letter you just read, a group of poachers follow you to take it from you. You can either attack them or give them the letter, fail the quest and they follow you again anyways. The issue here is that while the poachers are "Outlaws" the party itself they're in is "Neutral", and since you're in indifferent relations with the "Neutral faction", attacking them lowers relation with "Neutral" and you lose honor. The biggest problem here is that everything that's in the "Neutral" faction runs away from you. (Cattle won't ever accompany you, the spy you're following for the quest to catch him alive runs away from you, he doesn't head to the direction of his master etc.)
This is not really a bug but a minor mistake/misclick made by the dev. I've fixed this issue by modifying that Poacher party from "Neutral" to "Outlaw". Now when you attack them you don't lose honor or relations with Neutral - Instead, you lose relation points with the Outlaws, just like it's supposed to be in the first place.
If anyone wants to use it, you're free to download it from here.
tldr: Instead of losing honor and relation points with the Neutral faction for attacking the Poacher party, you should lose relations with the Outlaw faction instead. I've fixed this by editing "party_templates" located in AWOIAF folder.
(https://s32.postimg.org/3vetw08ud/you_get_this.png)
If you want to use the modified party_templates file, I've uploaded it as an attachment. Copy and replace to Modules/AWOIAF
I'm sorry it didn't change anything for me :(
This is in beta 10 changelog, next version will have this fixed, but as we don't know the release date, the temporal fix is welcomed :)