It failed to delete a collection when any inactive core appear in the collection. the inactive core due to a lot of reasons. usually caused by recovering failed and the inactive core hard to active again only if it have chance to be a leader. but for user, he/she doesn't care the core is active or not if he/she already decide to delete the collection. so we should delete the inactive core too rather than stop user doing this operation. this behavior lead a collection contained inactive core almost impossible to be deleted.