Hi,
this sounds to me like, when you put the throttles into reverse, they go instead to TO/GA, therefore the full thrust you are reporting. If my analysis is correct, check if there is some stock set up with your joystick that sends the throttles to TO/GA mode. I also do not want to exclude a bug with the new 11:30 version, which is a likely thing, and if the case, will be eventually reported by other users and fixed by Laminar Research.