There is a reason for that:
They trade nearly identically. I remember once preferring Brazil over China, and most of the time that has made sense. Brazil's markets have vastly outperformed China's since 2004. However, it appears that since the huge 2008 correction in all emerging market stocks (and all stocks for that matter) these two markets have been locked in a very tight dance. I know that the Brazilian exports to China are one of the primary drivers of economic growth in Brazil, but you would think that differentials in company performance would produce more variance than this.