While flying with a horse attached by lead, instead of the horse following into the air and falling, as I understand is the intention, the lead simply continued to get longer and the animal did not follow at all. Please see attached picture which shows the too long lead with no animal attached. I also do not believe that this particular issue has been addressed as I spent the better part of 30 minutes searching to make sure this wasn't a duplicate. I hope this helps!

EDIT: After returning to the world to continue testing this, the lead functioned properly. I have no idea why it did not do so in the instance shown in the picture, but figure it may be a random bug that sometimes shows up.