Hopper + Brewing Stand = Server Crash

Had 2 Brewing Stands next to each other.
One Hopper directly above each of them pointing down.
Put 3 Water Potions in each stand.
Put 1 nether wart, sugar, redstone in each hopper in quick succession.
Do something else for about 10 seconds.
[Server Connection Timeout] (or so)
Server Had Crashed.
Server throws exception each time I try to restart it.
Cannot reconnect or fix the server.
Exception attached.

This happened a second time in a new world on the server again with brewing stands + hoppers, but with a different potion recipe.

Tested with: Minecraft 1.6 (pre relase) + Launcher 1.0.2