Subscription to OFFER:after event ignores request for acknowledgement

The subscription to an OFFER:after event with acknowledgement

mstro_subscribe(selector, MSTRO_POOL_EVENT_OFFER, MSTRO_SUBSCRIPTION_OPTS_REQUIRE_ACK, &offer_subscription);

is expected to block the producer's OFFER until the an acknowledgement is sent

mstro_subscription_ack(offer_subscription, event);

However, this seems not to be the case, which may result in the producer's withdrawing the CDO before the REQUIRE is posted.