Hello !
I was experimenting with the new command /item before realising it is quit bugged (sorry for bad english btw)
So, the problem is that when dropping the item if ur not looking in the inventory, well the item just diseapears [and the command is in a repeat always ative command block with the right command]. It is still here, cause we can still press "Q" or "A" (depends on ur controls) and you will see an item drop on F5. Tho is it's for exemple a spyglass or something that is used in a ways or another, you can't use it anymore.
If you keep looking in ur inventory tho wathever you do it will still be here. So I'm sure it's a bug.
GL