/team join and /team leave tab-complete all entries currently stored in the scoreboard including fake players whose names start with #.
/team leave should only tab-complete the names of players / entities which are in the team (currently not the case unless the scoreboard tracks them as well).
(?) Maybe /team join should tab-complete the names of currently online players.
- Create a scoreboard objective and store a value for a fake player
- Type the following
→ It suggests #fakePlayer