Switching to spectator mode while fishing keeps rod cast

Confirmed.

Confirmed for 1.11.2

The following is based on a decompiled version of Minecraft 1.12 using MCP 9.40pre-1. (By the way, 1.12 should be marked as affected here)

The method net.minecraft.entity.player.EntityPlayerMP.setGameType() doesn't invoke the method net.minecraft.entity.player.EntityPlayerMP.fishEntity.handleHookRetraction() which removes the fish hook entity from the player's world and returns the amount of damage which should be applied to the fishing rod after its retraction.

A simple solution to this issue would be to add this specific method invocation to the setGameType() method.

Suggested fix

public void setGameType(GameType gameType)
{
    // ...

    if (gameType == GameType.SPECTATOR)
    {
        this.func_192030_dh();
        this.dismountRidingEntity();
        if(this.fishEntity != null) {
            this.fishEntity.handleHookRetraction();
        }
    }
    else
    {
        this.setSpectatingEntity(this);
    }

    // ...
}

if(this.fishEntity != null) checks if the player has casted a fish hook. Without this If-statement the game would throw a NullPointerException because it obviously can't remove a fishEntity that doesn't exist.

Can confirm in 20w51a.

Can confirm in 21w03a.

Can confirm for 21w42a.
When going to spectator the rods remain cast, also when left clicking you can still see the swing animation in the wire of the rod.
Also the sound that you have a fish hanging on the rod can still play.

Affects 1.18.1

Can confirm in 1.18.2.

Can confirm in 1.19.

Can confirm in 1.19.2.