I had the same issue. At some point however (towards the end of EA) I noticed it gave me the option to tell Rath in the druid's grove about it. Didn't really result in anything of note, maybe bringing it to the attention of someone before you save Halsin will give something more meaningful?
Yes, I believe that this is an oversight and we're 'too late' at this point. My guess is if you tell him while Halsin is still in the camp you can do something about Kagha. (If you attack one of those two pricks in the inner druid grove after you already solved the goblin issue only they + the gnome druid outside and Kagha will turn hostile, so I think those are the Shadow Druid ones..)
Same in the GOG version, was able to "Send to Camp"
Works for me too but then it's stuck in the camp's chest...