When me and a friend were building a map I was trying to run some tests with redstone and I tried to through a block onto a wooden pressure plate and the item appeared and then fell through my screen and vanished it did the same in a different location not on a pressure plate.
How to fix
Using NBT-Edit I compared my Level.dat file with a new fresh one.
In NBT-Edit the Byte "CanPickUpLoot" was 1, instead of the default 0. (In NBT-Edit: Data > Player > CanPickUpLoot)
For multiplayer use the player.dat files
Related issues
duplicates
Attachments
Comments

Please provide some screenshots.
This is the closest I can get to a screenshot for you because it is only there for .5 of a second for me.
Can you try this in survival and see if it equipts in one of your armor slots by chance?
I took a diamond helmet and put it on. That worked, but when I thrugh it the server kicked me and said Internal Server Error so I Checked my consul and I got this Message. My server is not bukket it is a normal server.
WARNING] Failed to handle packet for Death2142zerg/127.0.0.1: java.lang.ArrayIndexOutOfBoundsException: 4
java.lang.ArrayIndexOutOfBoundsException: 4
at qx.b(SourceFile:1519)
at md.c(SourceFile:1214)
at qx.c(SourceFile:357)
at md.j_(SourceFile:540)
at qx.j_(SourceFile:200)
at iq.g(SourceFile:175)
at iv.a(SourceFile:199)
at eb.a(SourceFile:136)
at cg.b(SourceFile:349)
at iv.d(SourceFile:57)
at iw.b(SourceFile:39)
at ht.b(SourceFile:30)
at net.minecraft.server.MinecraftServer.r(SourceFile:762)
at ho.r(SourceFile:248)
at net.minecraft.server.MinecraftServer.q(SourceFile:679)
at net.minecraft.server.MinecraftServer.run(SourceFile:613)
at fy.run(SourceFile:849)
[INFO] Death2142zerg/127.0.0.1:60708 logged in with entity id 1019 at (25.1215265934321, 101.0, 37.06370543433935)
[WARNING] Failed to handle packet for Death2142zerg/127.0.0.1: java.lang.ArrayIndexOutOfBoundsException: 4
java.lang.ArrayIndexOutOfBoundsException: 4
at qx.b(SourceFile:1519)
at md.c(SourceFile:1214)
at qx.c(SourceFile:357)
at md.j_(SourceFile:540)
at qx.j_(SourceFile:200)
at iq.g(SourceFile:175)
at iv.a(SourceFile:199)
at eb.a(SourceFile:136)
at cg.b(SourceFile:349)
at iv.d(SourceFile:57)
at iw.b(SourceFile:39)
at ht.b(SourceFile:30)
at net.minecraft.server.MinecraftServer.r(SourceFile:762)
at ho.r(SourceFile:248)
at net.minecraft.server.MinecraftServer.q(SourceFile:679)
at net.minecraft.server.MinecraftServer.run(SourceFile:613)
at fy.run(SourceFile:849)
[INFO] Death2142zerg/127.0.0.1:60713 logged in with entity id 1274 at (25.1215265934321, 101.0, 37.06370543433935)
[WARNING] Failed to handle packet for Death2142zerg/127.0.0.1: java.lang.ArrayIndexOutOfBoundsException: 4
java.lang.ArrayIndexOutOfBoundsException: 4
at qx.b(SourceFile:1519)
at md.c(SourceFile:1214)
at qx.c(SourceFile:357)
at md.j_(SourceFile:540)
at qx.j_(SourceFile:200)
at iq.g(SourceFile:175)
at iv.a(SourceFile:199)
at eb.a(SourceFile:136)
at cg.b(SourceFile:349)
at iv.d(SourceFile:57)
at iw.b(SourceFile:39)
at ht.b(SourceFile:30)
at net.minecraft.server.MinecraftServer.r(SourceFile:762)
at ho.r(SourceFile:248)
at net.minecraft.server.MinecraftServer.q(SourceFile:679)
at net.minecraft.server.MinecraftServer.run(SourceFile:613)
at fy.run(SourceFile:849)
Also When I opened my inventory I found a grass block in my foot slot and i took it out (that was just before I threw the helmet). After I took it out i tried to replicate and couldn't.
Exactly what I thought, duplicate of MC-4560.
Ok i will check there, and try to fix it from there i will also post a fix on this.