Description of the Bug

Server crash when using the train placer.

To Reproduce

Train placer facing up with rail (total length of 4 long) on top, have electric locomotive with 1 cart as pattern, have the trains and carts inside the buffer.
Given a redstone signal will place the locomotive then crash.

Logs & Environment

• Full log:
  https://gist.github.com/Naxanria/b376dd371f069c669df7fb50421a95f4
• Crash report (If available):
  https://pastebin.com/XhPBkb1c

Duplicate of #1592. Will be fixed in beta 5.