Entering spectator mode does not cause leads to become detached from the player, and thus they can still fly around and bring another entity with them.
From other players' perspectives, the end lead stays fixed at the location of the gamemode switch, but they still see the entity being moved as on the client.
TorNato
Thank you for your report!
We're tracking this issue in MC-99785, so this ticket is being resolved and linked as a duplicate.
If you would like to add a vote and any extra information to the main ticket it would be appreciated.
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