I think such price dumps are only possible when ICOs calculate the proportion of bounty unwisely. For instance, some ICOs don't shrink pools if they don't hit the hardcap which results in too many tokens allocated to bounty hunters most of whom are eager to fix their profit.
Yeah that's true, and I think that is why many ICOs have now decided to share a percentage of sold or minted tokens to bounty hunters. With that it allows a healthy pool if the tokens to be given to hunters.