Either way the stock price is influenced. In the first case, supply of the share is increased by the fact that A sells B's share, and in the second case, demand

Either way the stock price is influenced. In the first case, supply of the share is increased by the fact that A sells B's share, and in the second case, demand is decreased by the fact that instead of buying a share B buys a contract to have A deliver a share at a later time. Why is this a problem?