yet another dupe bug [server only]

It happens on plain forge server

Issue Description:

Any crafting that involves a backpack on the crafting grid. You pick the items in and out off the grid. You see that items start to duplicate, you pick one item but there is a second one that remains on the grid. Then you close the inventory (press E or ESC).

Some items got dropped, Some items remain on your inventory, almost guaranteed dupe.

What happens:

You can duplicate backpacks (filled with dirt) almost systematically

What you expected to happen:

Nothing. Items that you've picked with the mouse fall on the ground, while those that were on the crafting grid, go back to your inventory.

Steps to reproduce (important):

Put a gray dye on the inventory's crafting slot (bottom left corner)
Put a backpack full of dirt on the crafting slot next to the above mentioned dye (bottom right corner)
Click with the right mouse button lots of times, one time on one slot, and right next on the other one (yes, like flipping the recipe back and forth) ...

Affected Versions (Do not use "latest"):

IronBackpacks: IronBackpacks-1.12.2-3.0.8-12
Minecraft: 1.12.2
Forge: forge-1.12.2-14.23.5.2838-universal

I get a stacktrace on the server. It looks like there is an error on the recipe to dye backpacks so that crash does something with wrong with concurrency and here we go:

[22:02:41] [Server thread/FATAL] [net.minecraft.server.MinecraftServer]: Error executing task
java.util.concurrent.ExecutionException: java.lang.BootstrapMethodError: java.lang.NoSuchMethodError: 
    at java.util.concurrent.FutureTask.report(Unknown Source) ~[?:1.8.0_261]
    at java.util.concurrent.FutureTask.get(Unknown Source) ~[?:1.8.0_261]
    at net.minecraft.util.Util.func_181617_a(SourceFile:47) [h.class:?]
    at net.minecraft.server.MinecraftServer.func_71190_q(MinecraftServer.java:723) [MinecraftServer.class:?]
    at net.minecraft.server.dedicated.DedicatedServer.func_71190_q(DedicatedServer.java:397) [nz.class:?]
    at net.minecraft.server.MinecraftServer.func_71217_p(MinecraftServer.java:668) [MinecraftServer.class:?]
    at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:526) [MinecraftServer.class:?]
    at java.lang.Thread.run(Unknown Source) [?:1.8.0_261]
Caused by: java.lang.BootstrapMethodError: java.lang.NoSuchMethodError: 
    at gr8pefish.ironbackpacks.core.recipe.ColorBackpackRecipe.getDyeColor(ColorBackpackRecipe.java:57) ~[ColorBackpackRecipe.class:1.12.2-3.0.8-12]
    at gr8pefish.ironbackpacks.core.recipe.ColorBackpackRecipe.func_77572_b(ColorBackpackRecipe.java:40) ~[ColorBackpackRecipe.class:1.12.2-3.0.8-12]
    at net.minecraft.inventory.Container.func_192389_a(Container.java:798) ~[afr.class:?]
    at net.minecraft.inventory.ContainerPlayer.func_75130_a(ContainerPlayer.java:88) ~[agi.class:?]
    at net.minecraft.inventory.InventoryCrafting.func_70299_a(SourceFile:93) ~[afy.class:?]
    at net.minecraft.inventory.Slot.func_75215_d(Slot.java:70) ~[agr.class:?]
    at net.minecraft.inventory.Container.func_184996_a(Container.java:327) ~[afr.class:?]
    at net.minecraft.network.NetHandlerPlayServer.func_147351_a(NetHandlerPlayServer.java:1162) ~[pa.class:?]
    at net.minecraft.network.play.client.CPacketClickWindow.func_148833_a(CPacketClickWindow.java:38) ~[lf.class:?]
    at net.minecraft.network.play.client.CPacketClickWindow.func_148833_a(CPacketClickWindow.java:12) ~[lf.class:?]
    at net.minecraft.network.PacketThreadUtil$1.run(SourceFile:13) ~[hv$1.class:?]
    at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source) ~[?:1.8.0_261]
    at java.util.concurrent.FutureTask.run(Unknown Source) ~[?:1.8.0_261]
    at net.minecraft.util.Util.func_181617_a(SourceFile:46) ~[h.class:?]
    ... 5 more
Caused by: java.lang.NoSuchMethodError: 
    at gr8pefish.ironbackpacks.core.recipe.ColorBackpackRecipe.getDyeColor(ColorBackpackRecipe.java:57) ~[ColorBackpackRecipe.class:1.12.2-3.0.8-12]
    at gr8pefish.ironbackpacks.core.recipe.ColorBackpackRecipe.func_77572_b(ColorBackpackRecipe.java:40) ~[ColorBackpackRecipe.class:1.12.2-3.0.8-12]
    at net.minecraft.inventory.Container.func_192389_a(Container.java:798) ~[afr.class:?]
    at net.minecraft.inventory.ContainerPlayer.func_75130_a(ContainerPlayer.java:88) ~[agi.class:?]
    at net.minecraft.inventory.InventoryCrafting.func_70299_a(SourceFile:93) ~[afy.class:?]
    at net.minecraft.inventory.Slot.func_75215_d(Slot.java:70) ~[agr.class:?]
    at net.minecraft.inventory.Container.func_184996_a(Container.java:327) ~[afr.class:?]
    at net.minecraft.network.NetHandlerPlayServer.func_147351_a(NetHandlerPlayServer.java:1162) ~[pa.class:?]
    at net.minecraft.network.play.client.CPacketClickWindow.func_148833_a(CPacketClickWindow.java:38) ~[lf.class:?]
    at net.minecraft.network.play.client.CPacketClickWindow.func_148833_a(CPacketClickWindow.java:12) ~[lf.class:?]
    at net.minecraft.network.PacketThreadUtil$1.run(SourceFile:13) ~[hv$1.class:?]
    at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source) ~[?:1.8.0_261]
    at java.util.concurrent.FutureTask.run(Unknown Source) ~[?:1.8.0_261]
    at net.minecraft.util.Util.func_181617_a(SourceFile:46) ~[h.class:?]
    ... 5 more

gr8pefish / IronBackpacks