lebnjb,
My comments were based on what I think I may have read many years back but I have not validated or confirmed the same.
The question for your broker is if/how can you prevent the shares you hold from being 'shorted'. (i.e.) Loaned to someone else who intends to sell them and buy them back at a lower price, hence making a profit and then returning the original borrowed shares.
But perhaps someone here knows more???