I saw a few discussions on this but so I thought I would just post for my solution (obvious in hindsight).

You have an application with states, you mediate view components in each state and within that mediation you add signal dispatch method handlers in the onRegister - flipping between states causes a build up method handlers i.e. you see the same methods being called multiple times.

The solution for me was to use the onRemove method of the mediator to remove the method handlers from the signal.