Changing the host's game mode in a world open to LAN changes the guests' default game mode

Due to the changes made recently, gamemode and defaultgamemode have become extremely inconsistent, inconvenient and incomprehensible. I am going to explain all the different scenarios that cause unexpected behavior in a series of tickets after I lay down the expected behavior. These were all covered in a single ticket by another user, which was resolved because it was invalid due to multiple bugs in one ticket.

Terminology

• World visibility state

  • Singleplayer: A world that is created through singleplayer world creation, is NOT open to LAN only housing a single player.

  • Open to LAN: A world that is created through singleplayer world creation, but is opened to LAN. It houses 1 or more players.

  • Multiplayer: A world that is created through dedicated server multiplayer world creation. It houses 0 or more players.

• Gamemode state

  • (Player) Gamemode: The gamemode of an individual player.

  • Default Gamemode: the default gamemode of the world which is traditionally modified with /defaultgamemode and shows up on the level select screen in singleplayer. (or in server.properties > gamemode=<GAMEMODE> for servers)

  • LAN Gamemode: the temporary default gamemode which applies only in Open to LAN worlds to other players.

  • Forced Gamemode: the gamemode to switch players to upon joining. Found in server.properties force-gamemode=<bool>

Expected

• as a host player, changing my own gamemode during open to LAN session should not change the defaultgamemode/open to lan gamemode. any guest players joining should not copy my gamemode, but follow the open-to-lan override/defaultgamemode.

Actual

• Changing the host’s gamemode during an open to LAN session modifies the open-to-lan gamemode (if it wasn’t modified) as well as the default gamemode. If I changed the open-to-lan gamemode, it will seemingly no longer change this through /defaultgamemode or /gamemode. (not expected)

• ANY PLAYER INCLUDING GUESTS and datapacks could run /gamemode for the host, thus changing the defaultgamemode through proxy.

Please check the attached video. It explains many of the issues found in the post I am copying from (but not all), as it visually shows many of these scenarios. Minecraft Game Modes Are More Complex Than Quantum Mechanics...