I was dragging a horse and 2 donkeys while riding a boat across the ocean. After riding about 200 blocks across, I began to notice the leads stretch noticeably over their 10 block limit. After about another 100 blocks the animals appeared about 30 blocks away and would not be dragged towards me when i stopped the boat. The boat, however, would get bumped around as if the horse and donkeys were right next to me. (basically indicating a discrepancy between their actual location and their rendered location) The leads still did not break; however, upon pressing LSHIFT and dismounting the boat, i was teleported to the animals' location, leaving the boat where it was. The leads then broke.