OS: Windows 7 (ver 6.1, arch amd64)
Java: 1.8.0_25 (by Oracle Corporation)
Launcher: Minecraft Launcher 1.6.61 (bootstrap 100)
Minecraft: 16w39c (updated Fri Sep 30 16:13:34 CEST 2016)
title says it all.
Steps to reproduce:
Make an observer line over several thousand blocks and update the first one. The game crashes for me everytime