afaik it is kind of addressed in a note under FLAPS 2.......SELECT in FCOM-PRO-NOR-Approach-Aircraft Configuration Management-Intermediate/Final Approach
- When the speed brakes are deployed, extending the flaps beyond FLAPS 1 may induce a slight roll movement, and in calm conditions a small lateral control asymmetry may remain until disturbed by a control input or by an atmospheric disturbance.