The Bug:
Players become the controlling passengers of unsaddled camels when mounting them while other players are already riding them.
Steps to Reproduce:
Summon a camel without a saddle.
/summon minecraft:camel ~ ~ ~ {NoAI:1b}Get two players and label them "Player A" and "Player B".
Have "Player A" mount the camel to become its controlling passenger (the passenger that's responsible for the movement of the camel).
Get "Player B" to mount the same camel.
Get both players to observe who the controlling passenger now is.
Take note as to whether or not players become the controlling passengers of unsaddled camels when mounting them while other players are already riding them.
Observed Behavior:
Players become the controlling passengers of unsaddled camels when mounting them while other players are already riding them.
Expected Behavior:
Players would not become the controlling passengers of unsaddled camels when mounting them while other players are already riding them, following the behavior when players mount boats.
I can confirm this behavior.