Last night, Me and Kharjo got bored. So I decided I would finally show him the Soul Cairn and we would go search for the rest of Jiub's Opus. So we went to Castle Volkihar and snuck in the side door and what not, but when we got inside I hear Serana say "I knew I heard somebody" and then she proceeded to ice spike a death hound in the face. It was strange because she should have been waiting at Fort Dawnguard like usual. I thought nothing of it, Kharjo and Serana both followed me until Kharjo suddenly disappeared somewhere inside Volkihar and i was left with Serana as my follower. It was strange, I didn't dismiss anyone and I didn't ask her to follow me, but she did and she was legitamitely following me, I could make her wait, carry stuff, all that. But Kharjo was gone, and that kind of upset me. So I ran around the Soul Cairn for a bit with Serana, found the remaining pages of the Opus and returned to Tamriel. When we got back to Skyrim it was just me and Serana for a while, I didnt know what became of Kharjo, I was worried maybe he died, or got glitched right out of the game. Serana and I arrived in Solitude after a short walk from Volkihar and I turn around and there's Kharjo!

So I now have 2 followers, Serana and Kharjo!! I don't know if it was supposed to happen like that (highly doubt it), am I not allowed to bring another follower in the Soul Cairn or something? It seems really weird to have 2 followers but i'm not complaining.

Has this ever happened to anyone else? Im on 360, so obviously no mods made this happen.

wrong forum likely.

However I was using the UFO mod allowing me to take Serana and a follower at the same time. When I did the quest getting me into the Soul Cairn the first time, my follower would not progress past the door into the garden with the sun dial puzzle. I think its to prevent you from taking anyone other then Serana into the Soul Cairn.

When I finished the Soul Cairn quest and got the scroll, my follower met up with me outside the door she had been waiting at the whole time.

Isn't she just following until you give her the scroll that she asked for? If this is what I think it is you haven't completed the quest.