As it currently, moving dwellers to training rooms (when the room is already full) works exactly the same as it does with the production rooms: they will switch places with the dweller already in that room with the lowest stat related to that room.
This is wrong.
For example, I have 2 dwellers training their Strength, and 2 dwellers training their Perception. One from each room reaches the max level, while the other in each of the rooms isn't maxed yet.
If try to move the dweller with maxed Strength to the Armory room they're going to swap places with the dweller who isn't maxed yet.
This can make the gameplay enormously frustrating.
With the training rooms, it needs to be the other way around: moving the dweller with maxed Strength to the Armory room should make them switch places with the dweller with the highest Perception, rather than the dweller with the lowest Perception.