Affects Version/s: Minecraft 1.9
Fix Version/s: None
Environment:Windows 10: 64 bit
Java 64 bit version 1.8.0_25
If /give gives you an item, like a stone block, the same tick you click on that item, like another stone block, you don't get the /give item.
I was making a command block array that replaces splash potions when you use them when I encountered this bug.
Chained together, place three command blocks.
The first, a repeating command block with this command:
The second, a chain command block with this command:
and the third, also chain, with this
Clear your inventory, then set the first command block to "Always active".
After setting the repeat block to "Always active", you will be given a stone.
Click on that stone to pick it up, and you will be given another, but it won't appear in your inventory. Delete the stone under your cursor, and place a dirt in your first inventory slot, and you will be given another stone that will show up in your inventory this time.
This illustrates that after failing to receive the second stone, part of minecraft thinks it is in your first inventory slot. but when you place an item in that slot, minecraft realises that there isn't a stone there, and gives you a replacement as the command blocks dictate.
This bug doesn't happen on survival, unless you do it with a splash potion, and throw it (to splash it) instead of clicking it.
Probably related to MC-91661