Hard crash when placing pumpkin to test auto-farm, server will not restart

A user on our snapshot playtest server was building an auto harvesting pumpkin farm. They placed a pumpkin to test their circuit and the server crashed.

The server now crashes on start. Here is a summary of the (attached) crash report:

java.lang.ClassCastException: bgf cannot be cast to bgi
	at bay.a(SourceFile:37)
	at bau.b(SourceFile:116)
	at bhu.a(SourceFile:208)
	at sh.b(SourceFile:564)
	at avj.a(SourceFile:78)
	at sh.r_(SourceFile:550)
	at sh.k_(SourceFile:213)
	at net.minecraft.server.MinecraftServer.w(SourceFile:696)
	at rs.w(SourceFile:367)
	at net.minecraft.server.MinecraftServer.v(SourceFile:629)
	at net.minecraft.server.MinecraftServer.run(SourceFile:534)
	at java.lang.Thread.run(Thread.java:748)

I have attached the crash report. I am happy to publish the world file, if required, but it is over the 10 MB attachment limit.