All the bounty campaign that I've participated in has that kind of rules, although you do not want to have it you have no choice but to comply since ICO is both risky for the developers and bounty managers they need flexibility in implementing, I just don't like it when they delay the payment or lock the token.
delaying distribution and locking tokens instead of several projects also provides rules at the beginning. indeed they usually don't keep it, and sometimes it takes longer to distribute. during the project it was still running well and waiting because of development problems I didn't think there were any problems. it became understandable for all participants.