Why madara did not change after 1 and 8 tails was extracted from him?
From the Wiki, 


  Obito stabs Madara and manages to steal fragments of the One-Tail's and Eight-Tails' chakra from him before using Kamui to escape with Naruto.


Obito only took a small fragment, not the entire beast.

ref: http://naruto.wikia.com/wiki/Madara_Uchiha