I think this post explains why there has been so much selling...

I think this post explains why there has been so much selling pressure.

http://www.jsmineset.com/2013/09/20/the-gold-index-game/

Quote:
"If a company is dropped by secret decision of the members of the exchange on the index committee then all the following (tracking) funds have to sell on the same day. Since a tracking fund must track it cannot buy or sell early or late. If the tracking fund did then it would not be tracking for those early execution days in violation of its prospectus.

Member’s temptation to sell the shares short to the tracking funds that must buy then buy the companies from the tracking funds that must liquidate, as a product of a drop from the index, might be bought to cover their shorts. This temptation must be huge in the dark time in finance. There is generally a week between declaration of index fund and the day the tracking fund must buy or sell. It certainly explains the huge volume contra trend short term moves that take place exactly on the day tracking funds must ask."

Which perfectly explains the short selling pressure in the days before the index rebalancing and the huge volume on the day of the rebalancing.