A few blinking redstone lamps cause lagg, then hangs client 170 blocks far from the lamps

A player made a simple shop advertisement using redstone lamps near spawn.
There are no known issues except on a stripe of blocks.
177 block far to the north of the lamps the stripe capture players.
Connect to the included server, then walk to x=0, z=-180
Expect hanging your client, since the server goes fine.