What happens when Naix the Lifestealer infests one of Pandaren Brewmaster's spirits?
Solution 1:
If you infest before Primal split, N'aix will be infested in the Earth spirit. If you infest after Primal split and if I remember correctly, you can target any of the spirits with infest. In any case after primal split stop and when spirits reunite, N'aix is infested in brewmaster.
DotaCinema tested this in one of their mythbuster episode but I cant remember which one. Ill search for you when I go back home if you're interested. (Here's the link http://www.youtube.com/playlist?list=PLF50cvv4MhVp_ErjuMdZ1koG2MZxIm_Vf)