Snapshot 13w16a, Snapshot 13w19a, Snapshot 13w21a, Minecraft 1.6.1, Minecraft 1.6.2, Minecraft 14w08a, Minecraft 1.7.5
Windows XP, Java 7
You cannot place a block on the top of a fence with a leash tied to it without first removing the leash.
Steps to reproduce:
1. Place a Fence.
2. Attach a leash to it.
3. Attempt to place a block on the top of the fence.