They will automatically place a PB (payback) and PR if applicable (Partial Reserve = Partial Payback) on your subsequent RSV days in the current month. If you don't have sufficient RSV days remaining to soak up the PB/PR days, then they will be placed in your Bank for use at a later time.

You don't have the option to bank the days. It is simply a function of whether you have any RSV days left or not. It is NOT however automatic. Make sure you keep an eye on the PB/PR/Bank days, as a scheduler has to manually update your schedule/bank, and I've had to call them on it probably 1 in 5 times to have them process it correctly.