Server will process moves from client with bReplicateMovement set to false

UCharacterMovementComponent::ReplicateMoveToServer checks IsReplicatingMovement before sending moves to the server, but the server does not check IsReplicatingMovement when processing these received moves.
If a client locally sets bReplicateMovement to true while this value is false on the server, it will send its movement to the server. While the server won't replicate any of this character's movement to simulated proxies, it will still receive and process these moves as normal.

On the server, set bReplicateMovement to false for a client's character.
After this change has been received on the client, set bReplicateMovement to true locally on that client.
Observe the client moving locally as well as on the server.