CONF iture,rudderrudderrat
1. If ATHR is disengaged from ID button thrust needles will catch up with the doghnut where ever they are. To CLB if levers are in CLB. That is why you set it prior to disconnect.
2. If ATHR is disconnected from FCU, thrust will freeze in the present with thrust lock and ECAM warning.
3. If ATHR fails it will freeze with Thrust lock and ECAM.
The FOB in question is very old. ACNav is unable to digest it.
All this will invite another comment from bubbers44. That is his priviledge but it is not possible to conduct type rating through this channel.