In both cases, you are obligated to tack and round the mark, so if it comes out in a protest that you were sailing to Timbucktoo because your jib was jammed in a cleat, you might have a problem. Wind and sea conditions certainly play into any decision on whether you sailed too far before tacking, which is why I say it really needs to be heard in front of an experienced jury to get a more definitive answer.
Although it may be necessary in order to sail the course, no rule specifically obligates a boat to tack at a mark. A boat (especially a catamaran) clear astern and slightly to windward certainly can prevent the other boat from tacking (provided her action does not break Rule 2). If the boats leave the zone then Rule 18 ceases to apply. If a boat sails beyond the "mark-room to which she is entitled", then she does not receive exoneration under rule 21. Those are important considerations, but a boat may legitimately drive another boat past a windward mark layline in order to gain a tactical advantage.
