So someone in the alliance just mentioned this.
When you play the events, like Invasion, Raid, etc, it doesnt auto assign classes, which is fine do it yourself I guess.
But when you go to set a class, it says Change, which leads you to the understanding a class is already assigned.
Instead, why not change the wording to Assign.
This works on both fronts, as you are assigning that class to that team. You dont need to change anything. While it is a chance in class per team, you are simply assigning each class to each team.