Pickup an item in any gamemode, put them in any slot (1 to 9) and change the gamemode to spectator.
Press Q to throw the item.
I know that spectator mode can't pickup items, but the problem isn't.
The problem is: spectator mode can throw items in pressure plates, for example.
I'll continue my bug searching now. Sorry for my english.
Linked issues
is duplicated by 12
MC-46433
Spectator drop item
Resolved
MC-46440
Dropping Items in Spectator Mode
Resolved
MC-46452
/give to someone in spectatot mode it drops the item on the ground and item cant be picked up
Resolved
MC-46549
Can drop item on spectator mode
Resolved
MC-46655
Spectator item bug
Resolved
7 more links
Confirmed.