I am trying to add a water heater and I am trying to autosize the heater maximum capacity but it says

Warning ** Water heater named WATER HEATERhas heater capacity set to AUTOSIZE but it is missing associated WaterHeater:Sizing object
   **  Fatal  ** GetWaterThermalTankInput: Errors found in getting thermal storage input. Preceding condition(s) causes termination.

However, the fatal error disappears when I hardsize the heater maximum capacity. I believe this is a OpenStudio bug, can anyone clarify ?