Flaps 1+f landing is the preferred landing configuration in case of reverser unlocked. So in this case according to the schematic shown in the FCOM, flaps would retract to 1 when speed decelerates to 100 kts. Wonder why? And this is the only scenario I can think of, after a lot of research, that this auto extention happens.
I think you have that backwards... Flap 1 for approach (but only when reverse deployed (IAE/PW)/4doors open (CFM) otherwise its a flap 3 approach.) Then when rolling out the flap will extend. Its in my bucket of 'who cares' because it isn't going to disturb anything at that stage during the landing roll and I hope to never see it in my career!!
Ed to add - I think the 100kt is there just to differentiate between departures (when you need 1+f) and arrivals (when only 1 is needed) when you have some more of the obscure Airbus style failures!!