The speculation that this huge overhang of positions would be unwound was behind the disruptions we saw following the Russian default and huge losses at hedge funds. Of course, there are as many purchasers as sellers in the market, and all positions sum to zero.
Nevertheless, the reaction of the market following a shock is dependent on who holds the positions,  BIS Review 84/1999  6  how concentrated the positions are, whether positions are correlated, etc.