Cannot get property as it does not exist

Server crashes due to "missing object." This crashes the server repeatedly after upgrade to 15w49a within a few minutes of logging in.

java.lang.IllegalArgumentException: Cannot get property arh

{name=half, clazz=class als$a, values=[top, bottom]}

as it does not exist in aqv

{block=minecraft:double_wooden_slab, properties=[variant]}

at aqv$a.c(SourceFile:165)
at als.k(SourceFile:50)
at aqv$a.q(SourceFile:388)
at ahu.a(SourceFile:203)
at ahu.a(SourceFile:132)
at lp.d(SourceFile:198)
at net.minecraft.server.MinecraftServer.D(SourceFile:617)
at la.D(SourceFile:339)
at net.minecraft.server.MinecraftServer.C(SourceFile:553)
at net.minecraft.server.MinecraftServer.run(SourceFile:457)
at java.lang.Thread.run(Thread.java:745)

This has also happened a few times with double_stone_slab and it seems to be related to slabs.