The lead that walked through walls

It was actually snapshot 13w26c, but the system didn't recognize the c

I had inadvertently kept hold of the lead for a tamed horse mob, entered my shelter and the lead passed through the wall and stayed intact.
Steps to Reproduce:
1. put a lead on a tamed horse mob outfitted with saddle and diamond horse armor
2. While holding the lead, enter a shelter constructed of obsidian with glass pane windows at head level alternating with obsidian and a glowstone roof/ceiling via a single iron door with button on outside and pressure plate inside
3. Walk back and forth and observe lead moving through the obsidian and glass.