I was playing around on a server with a minigame when I found accidentally this bug (so it works on multiplayer), managed to recreate it 100% of the time in singleplayer too.

Expected behaviour
Changing gamemode to spectator should reset the draw from the bow.

Actual behaviour
You are given the ability to shoot a single arrow in gamemode 3, which can be a powerful weapon in multiplayer.

Steps to recreate

1. Have any type of arrow in the offhand slot; potion tipped work as well. This step is essential, otherwise expected behaviour happens.
2. Draw back the bow
3. While still holding right click button, have your gamemode changed, either by combination of F3+n keys or by a command
4. Release right click button - arrow is shot from the bow, damaging its target
5. After changing gamemode back, you can notice 1 arrow from the stack was used, and the bow's durability dropped by a tiny amount.

I'm sorry for the title gore too, no idea how to word it better, or at least shorter,