When inside a nether portal, you cannot chat or open any menu. This makes it easy for other players to trap you inside a broken nether portal, preventing you from even leaving the server normally.
Players should always be able to open the main menu and the chat menu. The menus should also not close when the player is teleported, because this can also be used to trap players inside the server.
Please do not mark unreleased versions (anything starting with "Future Version") as affected. You don't know if it will be a problem in the future.