In singleplayer it works fine.
In multiplayer, if I try to craft 3 opened letters back to a piece of paper, as soon as I try to grab the paper from the slot the client crashes and the server shows this:
16:15:50 [WARNING] Failed to handle packet: java.lang.NullPointerException
java.lang.NullPointerException
at net.minecraft.server.ItemStack.<init>(ItemStack.java:24)
at net.minecraft.server.SlotResult.c(SlotResult.java:73)
at net.minecraft.server.Container.clickItem(Container.java:219)
at net.minecraft.server.NetServerHandler.a(NetServerHandler.java:1089)
at net.minecraft.server.Packet102WindowClick.handle(SourceFile:28)
at net.minecraft.server.NetworkManager.b(NetworkManager.java:251)
at net.minecraft.server.NetServerHandler.a(NetServerHandler.java:106)
at net.minecraft.server.NetworkListenThread.a(NetworkListenThread.java:8
2)
at net.minecraft.server.MinecraftServer.w(MinecraftServer.java:569)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:457)
at net.minecraft.server.ThreadServerApplication.run(SourceFile:492)
>
I have even tried this on a server containing ONLY Forestry