If you are seeing that your smaller bit is going over areas that have already been done by the larger bit, you may be running into this bug:
As a work-around, try this:
Instead of entering the the actual size of the previous bit, try entering (previous size - current size). In this case, since you are going from 1/16 to 1/32, change the previous size from 1/16 to 1/32 (i.e, half of what you have now).