After the ultimate of the Pandaren Brewmaster expires the spirits all unite back into his original form. Consider that one of these spirits has been Infested by Naix, The Lifestealer. What happens when the spirit expires? Does Naix automatically infest the Brewmaster, or is he left out in the open? If he is left out in the open, is his damage effect triggered or not?
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)