This excerpt taken from the C 10-K filed Feb 23, 2007.
Investments Sold Short
The Master Fund engages in short sales as part of its investment activities. The Master Fund is required to return securities equivalent to those borrowed for the short sale at the lenders demand. Pending the return of such securities, the Master Fund is required to deposit with the lender as collateral the proceeds of the short sale plus additional cash or securities. The amount of the required deposit is adjusted periodically to reflect any change in the market price of the securities that the Master Fund is required to return to the lender.