If an animal is traped somewhere while on a lead the lead will go through blocks.
What I expected to happen was...:
i thought the lead would break because it shouldnt pass through a block

What actually happened was...:
The lead passed through a block with no problems

Steps to Reproduce:
1.dig a 3x2x3 hole and put a horse in it
2. cove the top except for a little hole and hook the horse on a lead
3. put the other end of the lead on a fence
4.cover the rest of the hole

If it is had to understand the steps to reproduce i did make a video
Video: http://www.youtube.com/watch?v=rih63hO9kiA