The ECAM requests that the autothrust be disconnected because, currently, there is only one heated probe available and thus the parameters cannot be accurately compared to the unheated probes. My understanding is that, if not diconnected, then the autothrust will automatically disconnect some 90 seconds later.
This is on the earlier batch models. Batch 4 and above now need only one ADIRS source for the autothrust to work. The autothrust was thus removed from the staus list of inop items.....but the autothrust off line wasnt removed! Apparently, batch 6 and above will have this line removed.
In order to remain consistent with ECAM and tasksharing rules, airbus recommend that the autothrust is turned off when asked to BUT, when reading the inop items list on the status, since it doesnt appear here then the PF may reconnect it!