There is bound to be a drop in price WHENEVER Sellers are more willing to sell than buyers are willing to buy- simple supply-demand rule. In most cases ICO participants are given way more discounts than necesary, so they try to sell off and gain profit. Bounty hunters who gained coin almost free may be willing to sell off not considering the initial price of coin.
This is really true and I think this is the main reason for coin drop when listed. The bounty hunters sell at the rate they wish so as to sell and gain since the coin was gain for free. And few of the ICO use to do buy back to raise the price