Open Wesnoth, click on Multiplayer, select Host Networked Game. Host a game in that and have anybody (or nobody) join. Set a few players as AI, a few as localplayer.
The bug is in the control command - it is impossible to set a player to take control of a side controlled by the AI or by a localplayer. Commands that otherwise work perfectly in the MP server do weird things in the Network Game, so I suspect it's just a small bug - perhaps a mix-up with the control function and the leader renaming function.
You see, what does happen when we set "control 4 playername" is that it changes the leader's name. That is, the leader character and not the player name (which remains ai4 or anonymouslocalplayer4). What also happens is that control is wrested from ai4 or the local player, and once it's that player's turn, there is no way to continue the game as it is and we must quit.
