Hi DozyWannabe,
When A/THR is disengaged (or automatically disengages) then the thrust remains at the last setting prior to disconnect.
Only if "Thrust Lock" was activated.
The only way you'll end up in the situation you're describing is.....Or if they were in the climb detent at disconnect, you'd have to "jiggle" the levers and leave them in the climb detent/region - not recommended procedure in any aircraft, including "your" Boeing!
"Jiggling" is not necessary. Simply disengage auto thrust using the "instinctive disconnect buttons" on the T/Ls and you'd have set Climb Power.