You can no longer swim in water that is 1 block or less deep. I'm aware that this was technically listed as fixed on the changelog, but it needs to be brought back, and for a few reasons. Since we don't officially have crawling yet, this was used in conjunction with water logging to create entrances to houses that are 1 block tall, which you could swim through without fear of standing up and suffocating. It also made traversing small lakes easier, and getting through flowing water in caves less annoying. In short, it was useful, and not really a game breaking glitch