Duplication and deletion of ingredients, inventory desync and game freezing caused by faulty handling of firework star recipe

While crafting firework stars, I noticed that gold nuggets would duplicate themselves when clicking on them or on other items in survival, every now and then (see "Minecraft 18w11a - Bug gold nuggets.mp4"). Crafting was only possible one at a time (see the video), and while trying to fix it, it would recreate the items that I just used to craft (here, cyan dye and glowstone dust, but not the gunpowder!).

Additional experimenting revealed further issues: Items are being deleted, the way items are duplicated isn't the same depending on how you craft, inventory desync occurs; and the game can freeze when the crafting interface is closed after crafting, but without taking out the ingredients. See duplication1.mov, duplication2.mov, freeze.mov, desync.mov and deletion.mov for steps to reproduce these issues. For freeze.mov, note the way the gold nuggets keep getting placed in the hotbar. Once the escape menu is brought up from there, the game will freeze.

From the log:

23:55:01	net.minecraft.server.MinecraftServer	Server thread	fatal	Error executing task
java.util.concurrent.ExecutionException: java.lang.NullPointerException
	at java.util.concurrent.FutureTask.report(FutureTask.java:122)
	at java.util.concurrent.FutureTask.get(FutureTask.java:192)
	at k.a(SourceFile:147)
	at net.minecraft.server.MinecraftServer.w(SourceFile:671)
	at net.minecraft.server.MinecraftServer.v(SourceFile:627)
	at czd.v(SourceFile:155)
	at net.minecraft.server.MinecraftServer.run(SourceFile:532)
	at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.NullPointerException
	at arr.a(SourceFile:128)
	at amh.a(SourceFile:616)
	at amp.a(SourceFile:53)
	at amo.a(SourceFile:84)
	at ang.a(SourceFile:63)
	at amh.a(SourceFile:240)
	at tc.a(SourceFile:993)
	at mb.a(SourceFile:33)
	at mb.a(SourceFile:10)
	at in$1.run(SourceFile:13)
	at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at k.a(SourceFile:146)
	... 5 more