When you apply a Bell Schedule in the Calendar DAY, the DAY.BS column is still 0, even after you apply the Bell Schedule BSD Key to a day on DAY. So the FK from BSD to DAY is SC, BS, but DAY.BS is always 0.
Adding a Bell Schedule in the Calendar DAY, I think should record the BDS.KY into DAY.BS, but DAY.BS is always blank. Ticket Reference 308527