Guys you should take a look at this adress http://support.gamesas.com/eng/faqlist.asp
Its an faq of all problems in skyrim and dawnguard reported to bethesda, you could be surprised of their answer

have a look and have fun
for exemple:
Q My Vampire Lord drain life spell seems less powerful with Serana as a follower
A Serana has a negative effect on the Vampire Lord’s drain life spell while she is in your party. To work around this, avoid using Serana as a follower while in Vampire Lord form.
Q Cannot purchase the Alchemy Lab home improvement for Breezehome, the NPC simply takes your character’s money.
A This is a known issue and there is currently no workaround. If you require the use of an alchemy lab, you will need to find another (such as the one in Dragonsreach), or purchase one in a different home. Trying to buy it from the NPC will simply take the money without adding the improvement.
So dont hope any fix for the dlc